High-pressure X-ray Diffraction Experiments Research Articles

Studies on pressure-induced phase transition in zirconium

Abstract Pressure-induced phase transition in the IVa transition metal Zr has been studied by a high-pressure X-ray diffraction experiment and the superconductivity measurement under pressure. Two phase transitions from the h.c.p. to the hexagonal and further to the b.c.c. structure are observed at 6.7 and 33 GPa, respectively. An isostructural transition is also observed around 53 GPa in the b.c.c. phase. At the transition pressure of 33 GPa, the atomic volume of the b.c.c.-Zr agrees with that of the Va transition metal b.c.c.-Nb at zero pressure and the superconducting transition temperature also corresponds to that of the b.c.c.-Nb. These results are not only decisive evidence for the s-d transition in Zr but also suggest an idea of pressure-induced transformation from the IVa transition metal to the Va transition metal.

Pressure Effect of the Lattice Parameters for Mn2Sb and MnMGe (M=Al, Ga)

High-pressure powder X-ray diffraction experiments have been performed for Mn2Sb, MnAlGe and MnGaGe up to a pressure of 7.7 GPa at 300 K. Mn2Sb exhibits a discontinuous change in the lattice parameters a and c at about 3.5 GPa with increasing pressure. For MnAlGe and MnGaGe, the lattice parameters decrease linearly with increasing pressure.

Room‐temperature amorphlzation of fayalite and high‐pressure properties of Fe2SiO4 liquid

High‐pressure X‐ray diffraction and electron‐microscopy experiments show that fayalite (Fe2SiO4) transforms at around 350 kbar to an amorphous phase that can be quenched down to 1 bar. This room‐ternperature vitrification represents a thermodynamically driven fusion to a glass, as implied by the existence of a maximum above 100 kbar in the metastable extension of the melting curve of fayalite. The diffraction measurements, a thermodynamic analysis of the melting curve of fayalite, and the difference in bulk modulus between fayalite and Fe2SiO4 liquid are consistent with a reversible switch of silicon in the amorphous phase from a high coordination number at pressure down to 4‐fold coordination at 1 bar.

HIGH pressure structural investigations of zirconium using LMTO method

Abstract The structural energy differences have been calculated for zirconium as a function of pressure at zero temperature using the Andersen force theorem and the linear muffin tin orbital method. The structures included are the following: α (hcp), the room temperature room pressure phase, ω- a three atom simple hexagonal, bcc and fcc. Our calculations show that the bcc structure would become energetically most favourable above 11 GPa. This results is in agreement with well known correlation between the crystal structure and the d-electron population in transition metals at normal volume. The diamond anvil cell based high pressure x-ray diffraction experiments are in progress to verify this result.

High-pressure single-crystal studies of MnTiO3

Recent high-pressure single-crystal x-ray diffraction experiments have provided new information on the crystal chemistry of MnTiO3 and have provided insight into polymorphic transitions among phase...

The high-pressure equation of state of α-Mn to 42 GPa

High-pressure powder X-ray diffraction experiments have been done on alpha -Mn up to 42 GPa at room temperature with the use of a diamond anvil cell and a synchrotron radiation source. No structural phase transition has been found to 42 GPa with alpha -Mn remains the stable form. The atomic positions also do not change significantly with pressure, judging from the nearly constant intensity ratio of diffraction peaks. The compression data have been fitted to the Birch equation, yielding the isothermal bulk modulus and its pressure derivative as B0=131+or-6 GPa and B'0=6.6+or-0.7, respectively. The values of B0 and B'0 are discussed in relation to the local magnetic moment of alpha -Mn.

On the pressure-temperature phase diagram of the Kondo compound CeAl 2

Accurate high pressure X-ray diffraction experiments performed on a powdered single crystal of CeAl2 do not show any sizeable volume anomaly up to 150 kbar. However, high pressure electrical resistance experiments performed on a single crystal of the same batch show a continuous anomaly near 80 kbar at room temperature, i.e. close to the pressure for which Croft and Jayaraman [2] observed a strong volume anomaly. The resistance anomaly has been followed down to 2 K leading to a new line in the P-T diagram of CeAl2. This line, interpreted in terms of a crossover between two different Kondo regimes, crosses the critical line where magnetic order takes place. On the basis of our results in CeAl2, a detailed phase diagram for magnetically ordered Kondo compounds is proposed and discussed.

High pressure X-ray diffraction study on the structural phase transitions in PbS, PbSe and PbTe with synchrotron radiation

High pressure X-ray diffraction experiments have been performed on PbS, PbSe and PbTe up to 300 kbar with synchrotron radiation. PbS, PbSe and PbTe undergo pressure-induced first-order structural phase transition from NaCl-type (B1) phase to an intermediate phase at about 22, 45 and 60 kbar, respectively. Further structural phase transitions from the intermediate phase to the CsCl-type (B2) phase have been observed in PbS, PbSe and PbTe at about 215, 160 and 130 kbar, respectively. The crystal structures of the intermediate phases of these compounds are discussed.

High pressure X-ray diffraction study on the structural phase transition in MnS 2

High pressure X-ray diffraction experiments have been performed on MnS 2 with both conventional X-ray source and synchrotron radiation. MnS 2 undergoes a pressure-induced first-order structural phase transition from the cubic pyrite-type to the orthorhombic marcasite-type phase at about 140 kbar with about 15% volume contraction. Mn 2+ in the pyrite-type MnS 2 is in the high-spin state. The 15% volume contraction and the compressibilities of the two phases suggest a high-spin→ low-spin transition of Mn 2+ accompanying the structural phase transition.

Magnetic stirrer for diamond-anvil cells

A continuing problem in the performance of high-pressure X-ray diffraction experiments with a diamond-anvil cell is that of interpreting the integrated intensity data. Two primary causes of this are the relatively small number of crystallites in the pressure cavity and possible preferred orientation effects. An electromagnetic attachment has been designed and fabricated to provide a set of three orthogonal, time-varying magnetic fields at the pressure cavity. These are used to continually stir the contents of the pressure chamber when a hydraulic fluid is used. Integrated intensity data taken with this system using a synchrotron radiation source and energy dispersive detection techniques are presented.

Observation of the volume discontinuity in the insulator-to-metal transition in CsI in x-ray diffraction experiments.

We show that the volume discontinuity associated with an insulator-to-metal transition in CsI may not be observable in diamond-cell high-pressure x-ray diffraction experiments.

High pressure x-ray diffraction experiments on US using synchrotron radiation

High pressure X-ray diffraction studies (up to 40 GPa) were performed on US using synchrotron radiation and a diamond anvil cell. The measured value of 92 GPa for the bulk modulus B 0 is in reasonable agreement with calculations. The high pressure behaviour indicates a phase transformation to US III at about 15 GPa. The transformation is a smooth deformation process, which starts with a tetragonal structure ( a tetr = a cub 2 1 2 ; c tetr = 2 a cub ) and continues with an orthorhombic structure ( a = 375(3) pm; b = 345(3) pm; c = 1069(24) pm) at 35 GPa; it is second order within experimental error and it should involve some contributions from uranium f electrons.

Evidence for a Soft Phonon Mode and a New Structure in Rare-Earth Metals under Pressure

High-pressure x-ray diffraction experiments up to 30-40 GPa on lanthanum, praseodymium, and yttrium metals demonstrate that there is one more crystal structure in the regular rare-earth crystal-structure sequence. This structure results from a second-order phase transition in fcc phase and could be described by a zone-boundary soft phonon mode with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}}=(\frac{2\ensuremath{\pi}}{{a}_{0}})(\frac{1}{2}, \frac{1}{2}, \frac{1}{2})$.