We report structural and physical properties of the single crystalline . The X-ray diffraction (XRD) results show that adopts the trigonal -type structure. Temperature-dependent electrical resistivity measurements indicate an insulating ground state for with activation energies of 40 meV and 0.64 meV for two distinct regions, respectively. Magnetization measurements show no apparent magnetic phase transition under 400 K. Different from other , Sr, and Ba, and , As, and Sb) compounds with the same structure, heat capacity and reveal that has a first-order transition at and the transition temperature shifts to high temperature upon increasing pressure. The emergence of plenty of new Raman modes below the transition, clearly suggests a change in symmetry accompanying the transition. The combination of the structural, transport, thermal and magnetic measurements points to an unusual origin of the transition.

我们报告了单晶的结构和物理性质。X射线衍射（XRD）结果表明采用三角型结构。与温度相关的电阻率测量结果表明，对于两个不同的区域，激活能量分别为40 meV和0.64 meV时，绝缘基态处于绝缘状态。磁化测量显示在400 K以下没有明显的磁相变。不同于具有相同结构，热容量的其他Sr和Ba和As和As化合物，并显示在随着压力的升高，转变温度转变为高温。在过渡以下出现了许多新的拉曼模式，这清楚地表明伴随过渡出现了对称性的变化。结构，传输，热和磁测量的组合指出了转变的不寻常起点。