Structures and Phase Transitions of CePd_3+<i>x</i>Ga_8‑<i>x</i>: New Variants of the BaHg₁₁ Structure Type

New distorted variants of the cubic BaHg11 structure type have been synthesized in Ga flux. Multiple phases of CePd3+xGa8‑x, which include an orthorhombic Pmmn structure (x = 3.21(2)), a rhombohedral R3̅m structure (x = 3.13(4)), and a cubic Fm3̅m superstructure (x = 2.69(6)), form preferentially depending on reaction cooling rate and isolation temperature. Differential thermal analysis and in situ 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 BaHg11, 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 CePd3+xGa8‑x, the rare earth analogues REPd3+xGa8‑x, RE = La, Nd, Sm, Tm, and Yb, were successfully synthesized and also crystallize in one of the lower symmetry space groups.科研人员以镓助熔剂（Ga flux）成功合成了立方BaHg₁₁结构型的新型畸变变体。CePd₃₊ₓGa₈₋ₓ存在多个物相，包括正交晶系（orthorhombic）Pmmn空间群结构（x=3.21(2)）、三方晶系（rhombohedral）R3̅m空间群结构（x=3.13(4)）以及立方Fm3̅m超结构（x=2.69(6)），其优先形成行为取决于反应冷却速率与分离温度。差热分析与原位变温粉末X射线衍射图谱结果表明，在约640 ℃时，低温正交晶系、三方晶系结构与高温立方超结构之间存在可逆相变。单晶X射线衍射实验显示，BaHg₁₁的基本骨架（包含Ce原子呈笼目型（kagomé）排列的相交平面）在低温物相中仅发生轻微畸变。体系可能同时存在近藤效应（Kondo effect）、晶体电场效应（crystal electric field）与磁阻挫效应，进而导致磁化率、电阻率与热容测试中出现低温反常行为。除CePd₃₊ₓGa₈₋ₓ外，科研人员还成功合成了其稀土同系物REPd₃₊ₓGa₈₋ₓ（RE=La、Nd、Sm、Tm、Yb），该系列化合物同样结晶于低对称性空间群之一。