High-pressure synthesis, crystal structure and anisotropic thermal/compressive behaviors of pseudo-ternary (V,Cr,Mo)P4

Abstract

Pseudo-ternary CrP₄-type (V,Cr,Mo)P₄ was successfully synthesized at the conditions of 4 GPa and 900 °C by using a large volume multi-anvil-type press. SEM-EDS and STEM analyses revealed that the synthesized pseudo-ternary (V,Cr,Mo)P₄ contains almost equimolar amounts of transition metals. The lattice parameters and unit cell volume of (V,Cr,Mo)P₄ yield the average value of its end-members. The low-temperature (133 K–333 K) in-situ synchrotron XRD measurements demonstrated that the c-axis showed the highest coefficient of thermal expansion, followed by the b-axis and the a-axis. These thermal behaviors are the same as the binary end-members and pseudo-binary (V,Cr)P₄. While from the high-pressure (P < 10 GPa) in-situ synchrotron XRD measurements, it was found that (V,Cr,Mo)P₄ showed no phase transition and compression behaviors in which the c-axis was more compressible than the other two axes (b and a) and the b-axis was slightly compressible more than the a-axis. The zero-pressure bulk modulus of 106 (1) GPa and 122.1 (7) GPa were obtained for (V,Cr)P₄ and (V,Cr,Mo)P₄, respectively. MoP₆ octahedral is highly distorted in comparison with VP₄ and CrP₄, thus the incorporation of MoP₄ greatly yields incompressible behaviors of CrP₄-type phosphides with respect to temperature and pressure.