Comparing the compression behavior of the antiperovskites CePt3Si, CePt3B, and YPt3B from combined X-ray diffraction experiments and density functional theory

Abstract

In this study we report the synthesis three antiperovskites YPt3B, CePt3B, and CePt3Si as well a focused investigation of YPt3B, which all have the same P4mm symmetry with a large c∕a ratio at ambient conditions. The compounds are investigated under high-pressure using powder X-ray diffraction in diamond anvil cells. A structural transition is found to occur in the YPt3B compound at 23(2) GPa caused by the softening of a zone boundary phonon. Using a combination of symmetry analysis and structural prediction, the high-pressure phase is assigned to a structure described by the P2 (P121) space group. Calculation of the phonon dispersion confirms that this structure is dynamically stable with A = Ce, Y and Z = Si, B. It was found that the three APt3Z compounds behave differently with pressure. The bulk moduli for the three compounds are found to be 185(5) GPa, 155(3) GPa, and 128(2) GPa for YPt3B, CePt3B, and CePt3Si, respectively. We found that the Z atom moves away from the center with pressure for A = Ce along the c axis, whereas for A = Y, the Z atom stays in the approximately same position. This behavior is also reflected in their c∕a ratio which stays approximately constant in YPt3B. Overall we find that the Ce-bearing compounds are more compressible in the ab plane, reducing the tilting of the octahedra. As a result, in YPt3B and CePt3B the transition to the structure described by the P2 space group is likely to occur at higher pressures.