Structures and Phase Transitions
of CePd<sub>3+<i>x</i></sub>Ga<sub>8‑<i>x</i></sub>: New Variants
of the BaHg<sub>11</sub> Structure Type
- Publication date
- Publisher
Abstract
New distorted variants of the cubic BaHg<sub>11</sub> structure
type have been synthesized in Ga flux. Multiple phases of CePd<sub>3+<i>x</i></sub>Ga<sub>8‑<i>x</i></sub>, which include an orthorhombic <i>Pmmn</i> structure (<i>x</i> = 3.21(2)), a rhombohedral <i>R</i>3̅<i>m</i> structure (<i>x</i> = 3.13(4)), and a cubic <i>Fm</i>3̅<i>m</i> superstructure (<i>x</i> = 2.69(6)), form preferentially depending on reaction cooling rate
and isolation temperature. Differential thermal analysis and <i>in situ</i> temperature-dependent powder X-ray diffraction patterns
show a reversible phase transition at approximately 640 °C between
the low temperature orthorhombic and rhombohedral structures and the
high temperature cubic superstructure. Single crystal X-ray diffraction
experiments indicate that the general structure of BaHg<sub>11</sub>, including the intersecting planes of a kagomé-type arrangement
of Ce atoms, is only slightly distorted in the low temperature phases.
A combination of Kondo, crystal electric field, and magnetic frustration
effects may be present, resulting in low temperature anomalies in
magnetic susceptibility, electrical resistivity, and heat capacity
measurements. In addition to CePd<sub>3+<i>x</i></sub>Ga<sub>8‑<i>x</i></sub>, the rare earth analogues REPd<sub>3+<i>x</i></sub>Ga<sub>8‑<i>x</i></sub>, RE = La, Nd, Sm, Tm, and Yb, were successfully synthesized and
also crystallize in one of the lower symmetry space groups