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1 Jun 2012

Volume 111, Issue 11, Articles (11xxxx)

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J. Appl. Phys. 111, 112501 (2012); http://dx.doi.org/10.1063/1.4726137 (1 page)

Jiuhua Chen, Haozhe Liu, and Naurang L. Saini
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Preface to Special Topic: Selected Papers from the International Conference on the Study of Matter at Extreme Conditions, SMEC 2011

Jiuhua Chen, Haozhe Liu, and Naurang L. Saini

J. Appl. Phys. 111, 112501 (2012); http://dx.doi.org/10.1063/1.4726137 (1 page)

Online Publication Date: 15 June 2012

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01.30.Cc Conference proceedings
74.62.-c Transition temperature variations, phase diagrams

Structure and properties of superelastic hard carbon phase created in fullerene-metal composites by high temperature-high pressure treatment

O. Chernogorova, E. Drozdova, I. Ovchinnikova, A. V. Soldatov, and E. Ekimov

J. Appl. Phys. 111, 112601 (2012); http://dx.doi.org/10.1063/1.4726155 (5 pages)

Online Publication Date: 15 June 2012

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Treatment of a fullerene soot extract and metal (Co) powder mixture under pressure of 5 and 8 GPa at 1000 °C leads to the transformation of fullerites into superelastic hard phase (SHP) and to simultaneous sintering of the powder mixture to nonporous composite material reinforced by the SHP particles. The structure of the SHP particles reveals a topological relation to the initial fullerite crystal morphology. Upon indentation, the SHP particles demonstrate an elastic recovery of up to 96%. The universal microhardness of the SHP particles HU = 26 GPa, and their microhardness HV = 35 GPa. A high ratio between the microhardness and elastic modulus (HV/E = 0.19-0.21) of the SHP particles makes them perspective candidates for design of materials with superior wear resistance and tribological properties.
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61.43.Gt Powders, porous materials
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Pq Friction, lubrication, and wear
62.20.de Elastic moduli
62.50.-p High-pressure effects in solids and liquids

Electron localization in olivine materials for advanced lithium-ion batteries

L. Craco and S. Leoni

J. Appl. Phys. 111, 112602 (2012); http://dx.doi.org/10.1063/1.4726156 (5 pages)

Online Publication Date: 15 June 2012

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The olivines FePO4 and LiFePO4 are promising candidates for the next generation of lithium-ion batteries. Motivated thereby, we use a combination of first principles and many-body calculations to show the relevance of electronic correlations in these iron phosphate materials. We apply the theory to clarify relevant features seen in x-ray absorption and electrical transport experiments.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
82.47.Aa Lithium-ion batteries
71.15.-m Methods of electronic structure calculations
78.70.Dm X-ray absorption spectra
72.80.Sk Insulators

The role of Cu-O bond length fluctuations in the high temperature superconductivity mechanism

Guy Deutscher

J. Appl. Phys. 111, 112603 (2012); http://dx.doi.org/10.1063/1.4726157 (5 pages)

Online Publication Date: 15 June 2012

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We review three different kinds of experiments that emphasize the non-BCS, inhomogeneous aspects of superconductivity in the high Tc cuprates. The first is the existence of two different energy scales in the superconducting state, initially identified by a comparison between tunneling and Andreev–Saint–James spectroscopies [Deutscher, Nature (London) 397, 410 (1999)]. The second are EXAFS measurements of the Cu-O bond length distribution, which have shown that below a temperature T* > Tc, it becomes broader than expected from the Debye-Waller broadening and presents a split [Bianconi et al., Phys. Rev. Lett. 76, 3412 (1996)]. The third one is the effect of frozen lattice disorder on critical current and vortex pinning, which profoundly affects the pairing landscape [Gutierrez et al., Nature Mater. 6, 367 (2007)]. We then discuss how these results fit with models in which the electron-lattice interaction plays a leading role.
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74.40.-n Fluctuation phenomena
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
74.25.Sv Critical currents
74.50.+r Tunneling phenomena; Josephson effects
74.72.-h Cuprate superconductors
78.70.Dm X-ray absorption spectra

Isotope effect in the superconducting high-pressure simple cubic phase of calcium from first principles

Ion Errea, Bruno Rousseau, and Aitor Bergara

J. Appl. Phys. 111, 112604 (2012); http://dx.doi.org/10.1063/1.4726161 (5 pages)

Online Publication Date: 15 June 2012

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It has been recently shown [I. Errea, B. Rousseau, and A. Bergara, Phys. Rev. Lett. 106, 165501 (2011)] that the phonons of the high-pressure simple cubic phase of calcium are stabilized by strong quantum anharmonic effects. This was obtained by a fully ab initio implementation of the self-consistent harmonic approximation including explicitly anharmonic coefficients up to fourth order. The renormalized anharmonic phonons make possible to estimate the superconducting transition temperature in this system, and a sharp agreement with experiments is found. In this work, this analysis is extended in order to study the effect of anharmonicity in the isotope effect. According to our calculations, despite the huge anharmonicity in the system, the isotope coefficient is predicted to be 0.45, close to the 0.5 value expected for a harmonic BCS superconductor.
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74.25.Kc Phonons
63.20.Ry Anharmonic lattice modes
74.20.Fg BCS theory and its development
74.62.Yb Other effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

On determining the strength of the electron-phonon interaction from electron energy relaxation times

C. Gadermaier, V. V. Kabanov, A. S. Alexandrov, and D. Mihailovic

J. Appl. Phys. 111, 112605 (2012); http://dx.doi.org/10.1063/1.4726164 (3 pages)

Online Publication Date: 15 June 2012

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The strength of the electron-phonon interaction is most straightforwardly determined from electron energy relaxation times, provided that an appropriate relaxation scheme is assumed. We use literature data from fs spectroscopy on materials with different strengths of electron-phonon interaction to show that the commonly used two-temperature model is not suitable and a recently proposed non-equilibrium model should be used instead.
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63.20.kd Phonon-electron interactions
78.47.-p Spectroscopy of solid state dynamics
71.38.-k Polarons and electron-phonon interactions

High pressure Raman and x-ray diffraction studies on the decomposition of tungsten carbonyl

Subrahmanyam Garimella, Vadym Drozd, Andriy Durygin, and Jiuhua Chen

J. Appl. Phys. 111, 112606 (2012); http://dx.doi.org/10.1063/1.4726196 (7 pages)

Online Publication Date: 15 June 2012

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Polycrystalline tungsten hexacarbonyl, W(CO)6, was studied using in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD) at high pressures up to 60 GPa in a diamond anvil cell. High pressure causes collapse of the Oh molecular symmetry in W(CO)6 leading to decomposition of the carbonyl compound. The decomposed material has characteristic of δ(OCO), v(C=C), v(C=O), and adsorbed CO Raman features. High pressure XRD results showed the irreversible amorphization of tungsten hexacarbonyl. A solid state vibrational coupling mechanism is proposed to explain the formation of δ(OCO) units. Further, the high pressure Raman results of W, Mo, and Cr hexacarbonyls are compared and the breakdown of the Dewar-Chatt-Duncanson model in this family is qualitatively discussed.
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62.50.-p High-pressure effects in solids and liquids
78.30.Hv Other nonmetallic inorganics
68.43.Mn Adsorption kinetics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
63.20.-e Phonons in crystal lattices

Deformation of periclase single crystals at high pressure and temperature: Quantification of the effect of pressure on slip-system activities

Jennifer Girard, Jiuhua Chen, and Paul Raterron

J. Appl. Phys. 111, 112607 (2012); http://dx.doi.org/10.1063/1.4726200 (5 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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In order to investigate the effect of pressure on periclase (MgO) dislocation slip-system activities, creep experiments have been carried out on MgO single crystals, at T and P, respectively, ranging from 1000 °C to 1200 °C and 4 to 9 GPa, in a deformation-DIA apparatus coupled with x-ray synchrotron radiation. Crystals were deformed in compression along either [100], [100], or [111] directions. These orientations were chosen to activate, respectively, either 1/2〈1-10〉{110} dislocation slip systems, 1/2〈1-10〉{100} systems, or simultaneously 1/2〈1-10〉{110} and 1/2〈1-10〉{100} systems. Experiments are carried out in a temperature range of 1000 °C to –1200 °C and a pressure range up to 8 GPa. Experimental results indicate that pressure influences differently the activities of these slip systems, which should yield a transition of dominant slip systems from 1/2〈1-10〉{110} at low pressure to 1/2〈1-10〉{100}. This pressure induced transition is expected to occur at 23 GPa, which would correspond to a pressure in the top portion of the lower mantle.
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81.40.Lm Deformation, plasticity, and creep
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.20.Hg Creep
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

High-pressure behavior of osmium: An analog for iron in Earth’s core

B. K. Godwal, J. Yan, S. M. Clark, and R. Jeanloz

J. Appl. Phys. 111, 112608 (2012); http://dx.doi.org/10.1063/1.4726203 (5 pages)

Online Publication Date: 15 June 2012

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High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of osmium to over 60 GPa at room temperature. We find the zero-pressure bulk modulus in fair agreement with other experiments as well as with relativistic electronic band-structure calculations: Osmium is the densest but not the most incompressible element at ambient conditions. We also find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of osmium as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations but disagrees with recent claims that the electronic structure and equation of state of osmium exhibit anomalies at pressures of ∼15-25 GPa; the discrepancies are may be due to the effects of texturing.
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62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
71.20.Be Transition metals and alloys
61.66.Bi Elemental solids
64.30.Ef Equations of state of pure metals and alloys

Thermal conductivity of argon at high pressures and high temperatures

Alexander F. Goncharov, Michael Wong, D. Allen Dalton, J. G. O. Ojwang, Viktor V. Struzhkin, Zuzana Konôpková, and Peter Lazor

J. Appl. Phys. 111, 112609 (2012); http://dx.doi.org/10.1063/1.4726207 (6 pages)

Online Publication Date: 15 June 2012

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Knowledge of the thermal conductivity of Ar under conditions of high pressures and temperatures (P-T) is important for model calculations of heat transfer in the laser heated diamond anvil cell (DAC) as it is commonly used as a pressure transmitting medium and for thermal insulation. We used a modified transient heating technique utilizing microsecond laser pulses in a symmetric DAC to determine the P-T dependent thermal conductivity of solid Ar up to 50 GPa and 2500 K. The temperature dependent thermal conductivity of Ar was obtained by fitting the results of finite element calculations to the experimentally determined time dependent temperature of a thin Ir foil surrounded by Ar. Our data for the thermal conductivity of Ar are larger than that theoretically calculated using the Green-Kubo formalism, but they agree well with those based on kinetic theory. These results are important for ongoing studies of the thermal transport properties of minerals at pressures and temperatures native to the mantle and core.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
62.50.-p High-pressure effects in solids and liquids
02.70.Dh Finite-element and Galerkin methods
81.40.Gh Other heat and thermomechanical treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena

Pressure effects on strained FeSe0.5Te0.5 thin films

M. Gooch, B. Lorenz, S. X. Huang, C. L. Chien, and C. W. Chu

J. Appl. Phys. 111, 112610 (2012); http://dx.doi.org/10.1063/1.4726209 (4 pages)

Online Publication Date: 15 June 2012

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The pressure effect on the resistivity and superconducting Tc of prestrained thin films of the iron chalcogenide superconductor FeSe0.5Te0.5 is studied. Films with different anion heights above the Fe layer showing different values of ambient pressure Tc’s are compressed up to a pressure of 1.7 GPa. All films exhibit a significant increase of Tc with pressure. The results cannot solely be explained by a pressure-induced decrease of the anion height but other parameters have to be considered to explain the data for all films.
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62.50.-p High-pressure effects in solids and liquids
74.78.-w Superconducting films and low-dimensional structures
74.25.fc Electric and thermal conductivity

Pressure induced structural transitions in KH, RbH, and CsH

James Hooper, Pio Baettig, and Eva Zurek

J. Appl. Phys. 111, 112611 (2012); http://dx.doi.org/10.1063/1.4726210 (10 pages)

Online Publication Date: 15 June 2012

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The heavier alkali metal hydrides MH (M = K, Rb, Cs) undergo a series of pressure induced structural phase transitions: B1 (NaCl) → B2 (CsCl) → CrB. Experiments reveal that the latter occurs at 85 and 17.5 GPa for RbH and CsH, but it has not yet been observed for KH. Herein, evolutionary algorithms coupled with density functional theory calculations are employed to explore the potential energy surface of the aforementioned hydrides up to pressures of 300 GPa. The computations support previous theoretical work which predicts that KH will adopt the CrB structure when compressed. In addition, for KH and RbH we find configurations with Pnma and I41/amd symmetry that are thermodynamically competitive with the CrB structure at 300 GPa. Between 100–150 GPa, a Pnma structure which is analogous to a high‐pressure form of CsI is found to be the most stable phase for the heaviest alkali hydride considered. At higher pressures a hitherto unknown CsH–P63/mmc arrangement becomes thermodynamically preferred up to at least 400 GPa. A detailed analysis of the geometric and electronic structures of the various phases is provided.
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64.70.kp Ionic crystals
62.50.-p High-pressure effects in solids and liquids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.66.Fn Inorganic compounds

High P-T phase transitions and P-V-T equation of state of hafnium

Rostislav Hrubiak, Vadym Drozd, Ali Karbasi, and Surendra K. Saxena

J. Appl. Phys. 111, 112612 (2012); http://dx.doi.org/10.1063/1.4726211 (6 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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We measured the volume of hafnium at several pressures up to 67 GPa and at temperatures between 300 to 780 K using a resistively heated diamond anvil cell with synchrotron x-ray diffraction at the Advanced Photon Source. The measured data allows us to determine the P-V-T equation of state of hafnium. The previously described [Xia et al., Phys. Rev. B 42, 6736–6738 (1990)] phase transition from hcp (α) to simple hexagonal (ω) phase at 38 GPa at room temperature was not observed even up to 51 GPa. The ω phase was only observed at elevated temperatures. Our measurements have also improved the experimental constraint on the high P-T phase boundary between the ω phase and high pressure bcc (β) phase of hafnium. Isothermal room temperature bulk modulus and its pressure derivative for the α-phase of hafnium were measured to be B0 = 112.9 ± 0.5 GPa and B0′ = 3.29 ± 0.05, respectively. P-V-T data for the α-phase of hafnium was used to obtain a fit to a thermodynamic P-V-T equation of state based on model by Brosh et al. [CALPHAD 31, 173–185 (2007)].
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64.30.Ef Equations of state of pure metals and alloys
64.70.kd Metals and alloys
62.50.-p High-pressure effects in solids and liquids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Pressure-induced phase transition in potassium azide up to 55 GPa

Cheng Ji, Richard Zheng, Dongbin Hou, Hongyang Zhu, Jianzhe Wu, Ming-Chien Chyu, and Yanzhang Ma

J. Appl. Phys. 111, 112613 (2012); http://dx.doi.org/10.1063/1.4726212 (5 pages) | Cited 2 times

Online Publication Date: 15 June 2012

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Potassium azide was investigated by Raman scattering spectroscopy up to a pressure of 55.0 GPa by use of diamond anvil cell at room temperature. A pressure-induced reversible phase transition was revealed. The onset of the phase transition was characterized by the hardening of a previously soft lattice mode at 13.6 GPa. This transition is considered a structural phase transition. Compression induces a symmetry reduction, which is indicated by the splitting of the librational modes, the development of infrared active vibrational modes, and the appearance of other new modes in the external mode region. The new high-pressure phase, with azide ions still in a molecular state, can be preserved down to 1.2 GPa. The Grüneisen parameters for the parent phase were calculated.
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62.50.-p High-pressure effects in solids and liquids
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics

Pressure effects on unoriented and oriented single-walled carbon nanotube films studied by infrared microscopy

C. A. Kuntscher, A. Abouelsayed, K. Thirunavukkuarasu, F. Hennrich, and Y. Iwasa

J. Appl. Phys. 111, 112614 (2012); http://dx.doi.org/10.1063/1.4726214 (5 pages)

Online Publication Date: 15 June 2012

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We present the results of pressure-dependent infrared transmission measurements on films of oriented and unoriented single-walled carbon nanotubes. Up to the highest applied pressure (∼9 GPa), the optical response of the oriented single-walled carbon nanotube film is highly anisotropic, with strong absorption bands for the polarization of the radiation along the alignment direction due to optical transitions between the Van Hove singularities in the density of states. With increasing pressure, the optical transitions shift to smaller energies, with an anomaly in the pressure-induced shifts at 2–3 GPa related to the deformation of the nanotubes’ cross section. Weak signatures of a second anomaly are found at around 5–6 GPa, probably related to a more drastic deformation of the nanotubes. Different pressure transmitting media change the pressure-induced effects only quantitatively. The results for the oriented nanotube films are very similar to those for the unoriented ones.
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78.67.Ch Nanotubes
62.50.-p High-pressure effects in solids and liquids
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.30.Na Fullerenes and related materials
71.20.Tx Fullerenes and related materials; intercalation compounds

The structural stability of AlPO4-5 zeolite under pressure: Effect of the pressure transmission medium

Hang Lv, Mingguang Yao, Quanjun Li, Ran Liu, Bo Liu, Shuangchen Lu, Linhai Jiang, Wen Cui, Zhaodong Liu, Jing Liu, Zhiqiang Chen, Bo Zou, Tian Cui, and Bingbing Liu

J. Appl. Phys. 111, 112615 (2012); http://dx.doi.org/10.1063/1.4726222 (5 pages)

Online Publication Date: 15 June 2012

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The structural stability of AlPO4-5 zeolite (AFI) has been studied as a function of pressure up to 34.4 GPa in a diamond anvil cell by using synchrotron x-ray diffraction. It is found that the AFI structural stability can be enhanced significantly when a mixture of silicone oil and liquid nitrogen is used as pressure transmission medium (PTM). In this case, the crystalline-to-amorphous transition pressure for AFI increased to be 15.9 GPa, much higher than that of 8.5 GPa observed in the experiment by using silicone oil as PTM. We found that the average distance of the interplanar crystal spacing along to most planes was expanded obviously when liquid nitrogen is used as one component in the PTM. The presence of liquid nitrogen in the PTM also affects the structural evolution of the AFI channel under pressure. The results demonstrated that nitrogen molecules can be inserted into the channels of porous zeolite AFI single crystals, exerting a supporting effect against the structure collapse of AFI and thus improving their structural stability.
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61.43.Gt Powders, porous materials
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids

Manganese borides synthesized at high pressure and high temperature

Xiangxu Meng (孟祥旭), Kuo Bao (包括), Pinwen Zhu (朱品文), Zhi He (何志), Qiang Tao (陶强), Junjun Li (黎军军), Zhenpeng Mao (毛镇澎), and Tian Cui (崔田)

J. Appl. Phys. 111, 112616 (2012); http://dx.doi.org/10.1063/1.4726230 (5 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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We synthesized various kinds of manganese borides by liquid-solid reaction from manganese and amorphous boron powders at high pressure and high temperature. The mixed powders with various atomic ratio of boron to manganese, B/Mn = 0.6, 1.2, 2, 3, 4, 8, were treated at temperature 1100–1350 °C and pressure 4.8-5.5 GPa, for 10–285 min. Typical manganese borides such as Mn4B, Mn2B, MnB, Mn3B4, MnB2, MnB4, and MnBx were synthesized. MnB2 plays an important role in the reaction, which is the middle product and it changes to Mn3B4 and boron with increasing holding time at a mixed atomic ratio of B/Mn = 2 and MnB2 reacted with boron to MnB4 with increasing holding time at a mixed atomic ratio of B/Mn = 8. The preferred orientation of Mn3B4 was also obtained at a mixed atomic ratio B/Mn = 2 and whose growth is highly oriented. The crystalline phases MnB2, Mn3B4, MnB, and Mn2B were prepared with large excess boron content.
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81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
81.10.Dn Growth from solutions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
62.50.-p High-pressure effects in solids and liquids
61.66.Fn Inorganic compounds

Finite element calculations of the time dependent thermal fluxes in the laser-heated diamond anvil cell

Javier A. Montoya and Alexander F. Goncharov

J. Appl. Phys. 111, 112617 (2012); http://dx.doi.org/10.1063/1.4726231 (9 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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The time-dependent temperature distribution in the laser-heated diamond anvil cell (DAC) is examined using finite element simulations. Calculations are carried out for the practically important case of a surface-absorbing metallic plate (coupler) surrounded by a thermally insulating transparent medium. The time scales of the heat transfer in the DAC cavity are found to be typically on the order of tens of microseconds depending on the geometrical and thermochemical parameters of the constituent materials. The use of much shorter laser pulses (e.g., on the order of tens of nanoseconds) creates sharp radial temperature gradients, which result in a very intense and abrupt axial conductive heat transfer that exceeds the radiative heat transfer by several orders of magnitude in the practically usable temperature range (<12 000 K). In contrast, the use of laser pulses with several μs duration provides sufficiently uniform spatial heating conditions suitable for studying the bulk sample. The effect of the latent heat of melting on the temperature distribution has been examined in the case of iron and hydrogen for both pulsed and continuous laser heating. The observed anomalies in temperature-laser power dependencies cannot be due to latent heat effects only. Finally, we examine the applicability of a modification to the plate geometry Ångström method for measurements of the thermal diffusivity in the DAC. The calculations show substantial effects of the thermochemical parameters of the insulating medium on the amplitude change and phase shift between the surface temperature variations of the front and back of the sample, which makes this method dependent on the precise knowledge of the properties of the medium.
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79.20.Ds Laser-beam impact phenomena
66.70.Df Metals, alloys, and semiconductors
81.40.Gh Other heat and thermomechanical treatments
65.40.G- Other thermodynamical quantities
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.50.-p High-pressure effects in solids and liquids

Tetragonal to orthorhombic phase transition of ammonia borane at low temperature and high pressure

Shah Najiba, Jiuhua Chen, Vadym Drozd, Andriy Durygin, and Yongzhou Sun

J. Appl. Phys. 111, 112618 (2012); http://dx.doi.org/10.1063/1.4726236 (5 pages)

Online Publication Date: 15 June 2012

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The effect of pressure on the low temperature tetragonal (I4mm) to orthorhombic (Pmn21) phase transition of a potential hydrogen storage compound ammonia borane (NH3BH3) was investigated in diamond anvil cell using Raman spectroscopy. With applied pressure, the transition occurs at higher temperature, which indicates that pressure enhances the ordering of the structure. The positive Clapeyron slope of the transition was determined to be dP/dT = ∼25.7 MPa/K, indicating the transformation is of exothermic. Appearance of some of the characteristic Raman modes of orthorhombic phase requires undercooling of around ∼15 K below the transition, indicating possible existence of an intermediate phase.
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64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
78.30.Jw Organic compounds, polymers
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
88.30.rf Organics

Maintaining viability of white clover under very high pressure

N. Nishihira, T. Iwasaki, R. Shinpou, A. Hara, F. Ono, Y. Hada, Y. Mori, K. Takarabe, M. Saigusa, Y. Matsushima, N. L. Saini, and M. Yamashita

J. Appl. Phys. 111, 112619 (2012); http://dx.doi.org/10.1063/1.4726241 (4 pages)

Online Publication Date: 15 June 2012

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The high pressure technique developed in physics may give a new possibility if it is applied to a biological study. We have been studying the tolerance of small living samples such as planktons and mosses, and found that all of them were alive after exposed to extremely high hydrostatic pressure of 7.5 GPa. This technique has been extended to a higher plant Trifolium lepens L. (white clover). A few seeds of white clover were exposed to 7.5 GPa for up to 6 days. After the pressure was released, they were seeded on agar, or directly on sowing soil. Seventeen out of the total 22 seeds exposed to the high pressure were found to be alive. Those exposed for up to 1 day and seeded on agar germinated roots. Those exposed for up to 1 h and seeded on soil germinated stems and leaves. The present technique has the possibility of being applied to improve breed of plants and to discover a very strong species that stands against very severe environmental conditions.
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87.90.+y Other topics in biological and medical physics (restricted to new topics in section 87)

Fabrication of binary FeSe superconducting wires by diffusion process

Toshinori Ozaki, Keita Deguchi, Yoshikazu Mizuguchi, Yasuna Kawasaki, Takayoshi Tanaka, Takahide Yamaguchi, Hiroaki Kumakura, and Yoshihiko Takano

J. Appl. Phys. 111, 112620 (2012); http://dx.doi.org/10.1063/1.4726243 (3 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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We report successful fabrication of multi- and mono-core FeSe wires with high transport critical current density Jc using a simple in-situ Fe-diffusion process based on the powder-in-tube (Fe-diffusion PIT) method. The seven-core wire showed transport Jc of as high as 1027 A/cm2 at 4.2 K. The superconducting transition temperature Tczero was observed at 10.5 K in the wire-samples, which is about 2 K higher than that of bulk FeSe. The Fe-diffusion PIT method is suitable for fabricating multi-core wires of the binary FeSe superconductors with superior properties.
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81.20.-n Methods of materials synthesis and materials processing
74.25.Sv Critical currents
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
66.30.-h Diffusion in solids

Mechanism for reversible hydrogen storage in LiBH4–Al

Dorthe B. Ravnsbæk and Torben R. Jensen

J. Appl. Phys. 111, 112621 (2012); http://dx.doi.org/10.1063/1.4726244 (9 pages)

Online Publication Date: 15 June 2012

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A detailed investigation of the mechanism for the hydrogen release and uptake reactions in LiBH4–Al reactive composites by in-situ synchrotron radiation powder x-ray diffraction (SR-PXD) is presented. Different compositions of LiBH4–Al and the effect of the additive titaniumdiboride, TiB2, are investigated. This study reveals that dehydrogenation and rehydrogenation takes place via several reactions involving intermediate compounds and are more complex than previously anticipated. For the sample with high aluminum content (LiBH4:Al = 1:1.5), a reaction between molten LiBH4 and Al occurs at ∼340 °C to form LiH and an unknown compound, denoted 1. Upon further heating to ∼385 °C, lithiumaluminum alloy, LiAl, is formed from a reaction between LiH and Al and 1 transforms into a solid solution LixAl1−xB2. Rehydrogenation of the sample takes place in two steps with formation of LiH and Al at ∼260 °C and slow formation of LiBH4 and Al from LiH and LixAl1−xB2 at 400 °C using p(H2) = 100 bar for 1 h. For a sample with lower aluminum content (LiBH4:Al = 1:0.5) only partial dehydrogenation to LiH and 1 is obtained under similar conditions. The addition of TiB2 as catalyst to the sample of lower aluminum content (LiBH4:Al = 1:0.5) results in full dehydrogenation, i.e., formation of LiAl and LixAl1−xB2 again via 1 as intermediate. The presence of TiB2 seems to affect the reaction rates for the formation of LiAl and LixAl1−xB2. However, the lower amount of Al in these samples may cause formation of amorphous boron, hence only partial rehydrogenation is obtained under these relatively benign conditions (p(H2) = 100 bar, T = 400 °C).
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88.30.rd Inorganic metal hydrides

In-plane Cu–O bond distribution and charge inhomogeneity in La2−xSrxCuO4 as a function of doping

N. L. Saini, H. Oyanagi, T. Adachi, T. Noji, H. Sato, and Y. Koike

J. Appl. Phys. 111, 112622 (2012); http://dx.doi.org/10.1063/1.4726245 (4 pages)

Online Publication Date: 15 June 2012

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We report in-plane Cu–O atomic displacements as a function of doping in the La2−xSrxCuO4 system, determined by polarized Cu K-edge extended x-ray absorption fine structure measurements. We find a wide distribution of the Cu–O bonds showing a single peak asymmetric function for the system at low doping, which gets two peak function for the underdoped and optimally doped superconducting phases before turning to a single peak function for the overdoped phase. The results provide a direct evidence of critical local lattice fluctuations for an optimum transition temperature in the superconducting phases hosting quantum stripes.
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74.10.+v Occurrence, potential candidates
74.72.Cj Insulating parent compounds
74.40.-n Fluctuation phenomena
78.70.Dm X-ray absorption spectra
61.50.Lt Crystal binding; cohesive energy
74.62.Dh Effects of crystal defects, doping and substitution

Structure of jadeite melt at high pressures up to 4.9 GPa

Tatsuya Sakamaki, Yanbin Wang, Changyong Park, Tony Yu, and Guoyin Shen

J. Appl. Phys. 111, 112623 (2012); http://dx.doi.org/10.1063/1.4726246 (5 pages)

Online Publication Date: 15 June 2012

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The structure of jadeite (NaAlSi2O6) melts has been studied using multiple-angle energy-dispersive x-ray diffraction up to 4.9 GPa and 1923 K. The first sharp diffraction peak in the structure factor shifts toward higher momentum transfer as pressure increases, indicating the shrinkage of the intermediate network in the melt. The radial distribution function shows a monotonous decrease in average T-T length and T-O-T angle with increasing pressure, but displays no detectable change in the average bond length between tetrahedrally coordinated cations and oxygen (T-O length, where T = Si4+, Al3+). Our observations indicate that the dominant structural changes occur in the intermediate range order at pressures up to 4.9 GPa. The changes in T-O length, T-T length, and T-O-T angle appear to correlate with the viscosity anomaly in this pressure range.
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61.25.-f Studies of specific liquid structures
64.70.dj Melting of specific substances
62.50.-p High-pressure effects in solids and liquids

Similar behavior of thermoelectric properties of lanthanides under strong compression up to 20 GPa

Vladimir V. Shchennikov, Natalia V. Morozova, and Sergey V. Ovsyannikov

J. Appl. Phys. 111, 112624 (2012); http://dx.doi.org/10.1063/1.4726247 (9 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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We report results of investigations of thermoelectric properties of dozen of the lanthanides at ambient temperature under strong compression up to 15-20 GPa. We present data of pressure evolution of Seebeck coefficient in cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and ytterbium (Yb) and review literature data for lanthanum (La). Peculiarities detected at pressure dependencies of thermoelectric power were addressed to the known structural transitions. Therefore, thermopower values of all high-pressure phases below 20 GPa were established. Seebeck effect in different lanthanides subjected to compression demonstrated similar behavior: monotonic rising from near-zero values, ±(1-2) μV/K to magnitudes of ∼+(8-10) μV/K beyond about 5 GPa. This tendency was noticed in those rare-earth elements that follow a commonly accepted sequence of structural transformations for this group, and hence the s→d electron transfer is considered as a possible reason for this similar behavior of thermoelectric properties. Distinctive behavior of Seebeck effect in cerium and ytterbium may be related to peculiar structural phase diagrams of these elements. Possible implications from the findings of this thermoelectric study are discussed.
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72.15.Jf Thermoelectric and thermomagnetic effects
62.50.-p High-pressure effects in solids and liquids
81.30.Bx Phase diagrams of metals, alloys, and oxides
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
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