Polymorphic Phase Transformation in In2La and CeIn2

Abstract

Nuclear quadrupole interactions of 111Cd probes in In2La and CeIn2 were measured using perturbed angular correlation of gamma rays (PAC). Near room temperature, a single nonaxially symmetric quadrupole interaction was observed in each compound, with ω 0 = eQV zz /h = 78.8(2) Mrad/s and ŋ = 0.312(1) for In2La at 11 °C and ω 0 = 80(1) Mrad/s and ŋ = 0.29(2) for CeIn2 at 34 °C. The observed non-axial symmetry is consistent with the reported CeCu2 structure of the phases. The non-axially symmetric interactions were replaced completely by axially symmetric interactions (ŋ = 0) at 524 °C, with ω 0 = 101.0(1) Mrad /s in In2La and ω 0 = 96.9(4) Mrad/s in CeIn2. The change in symmetry is attributed to a polymorphic phase transformation. Based on symmetry information from the quadrupole interaction and on chemical arguments, it is proposed that high-temperature phases of In2La and CeIn2 both have the AlB2 (C32) structure.