C. S. Zha

Structure change of pyrochlore Sm2Ti2O7 at high pressures

Structural evolution of pyrochlore titanate Sm2Ti2O7 at high pressures was investigated by in situ Raman and x-ray diffraction methods. An intermediate phase was found at high pressures. The structure is a distorted pyrochlore, where anions are disordered after 40GPa while the cations are still somewhat ordered up to 51GPa. When the pyrochlore structure is severely distorted by external pressure, it transforms completely to an amorphous phase quenchable to room conditions.

Compression of Zr2InC to 52GPa

Using a synchrotron-radiation source and a diamond-anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Zr2InC sample. Up to a pressure of 52GPa, no phase transformations were observed. As observed in Ti3SiC2 and Ti3Si0.5Ge0.5C2, the compressibility of Zr2InC along the c axis was greater than along the a axis. The bulk modulus is 127±5GPa, with a pressure derivative of 4.25±0.3; the former is in excellent agreement with our ab initio calculations (130.9GPa). The a(3.367A) and c(15.100A) parameters from the ab initio calculations are also slightly larger than those measured here, viz., 3.35 and 14.91A. Surprisingly, a hysteresis was observed in the a-lattice parameters; they were higher upon unloading than loading. The reason for this hysteresis is not clear at this time.

Compression of Ti3Si0.5Ge0.5C2 to 53 GPa

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a polycrystalline Ti3Si0.5Ge0.5C2 sample. Up to a pressure of 53 GPa, no phase transformations were observed. As for the isostructural hexagonal Ti3SiC2, the compressibility along the c axis was greater than along a. The bulk modulus is 183±4u2009GPa with a pressure derivative of 3.4±0.2. This work shows that the replacement of Si by Ge in Ti3SiC2 results in a systematic decrease in the bulk moduli.

Compressibility and pressure-induced phase transformation of Ti3GeC2

In order to explore the large shear-strain-induced polymorph, α‐Ti3GeC2 polycrystals were investigated by using a synchrotron radiation source to 64GPa under nonhydrostatic state. Upon compression to 26.6GPa, α‐Ti3GeC2 starts to transform to β‐Ti3GeC2. As compared to α‐Ti3GeC2, the cell parameter a of β‐Ti3GeC2 is slightly shorter, and both c and c∕a larger. These two polymorphs exhibit similar compressibility. The bulk modulus is calculated to be 179(±10)GPa at a fixed K′=4.0. This is lower than that of Ti3SiC2, and close to that of Ti3Si0.5Ge0.5C2. The compressibilities of these two Ti3GeC2 polymorphs do not display an apparent anisotropy, and differ from the large anisotropies observed from Ti3SiC2 and Ti3Si0.5Ge0.5C2.