Multi-temperature X-ray diffraction study of a reversible structural phase transition in the high-temperature polymorph of Ce2Rh2Ga compound.

• Multitemperature X-ray study revealed a structural phase transition in HT-Ce 2 Rh 2 Ga. • Phase transition is accompanied by non-merohedral twinning. • Phase transition is reversible with a small hysteresis. • Interatomic distances abnormally increase when the sample is cooled below 145 K. • A strong NTE in the 85–112 K range with α = −2.588 10−4 deg−1 is found. A recently investigated HT-Ce 2 Rh 2 Ga was found to exhibit a magnetic phase transition at 128.5 K. A comprehensive multi-temperature investigation in the 85–400 K temperature range showed that the compound undergoes a structural phase transition as well. Upon cooling below 123.2 K its crystal symmetry changes from Cmce to C 2/ m being accompanied by non-merohedral twinning. Both structural transformations are reversible with a small hysteresis furthermore. The temperature of the structural phase transition was detected by anomalies in temperature dependences of unit cell dimensions, interatomic distances, and atomic displacement parameters. Negative thermal expansion along the c -axis was revealed in the range 92.7–170 K. When cooled to 200 K, Ce and Rh atoms converge to a distance sufficient for structural changes to become qualitative. Upon further cooling to 145 K, this interaction affects positions of all the atoms in the structure, leading to anisotropy of earlier equivalent interatomic distances and a sharp anomalous increase in atomic displacement parameters, the dynamics of which deviates more and more from the theoretical dependences in the Einstein and Debye approximations. [ABSTRACT FROM AUTHOR]