Li Yan, Cheng Jinguang, Alonso José Antonio, Goodenough John B, Zhou Jianshi
College of Materials Science and Engineering, Beijing Institute of Petrochemical Technology , Beijing 102617, China.
Materials Science and Engineering Program, University of Texas at Austin , Austin, Texas 78712, United States.
Inorg Chem. 2017 Jul 17;56(14):8187-8194. doi: 10.1021/acs.inorgchem.7b00864. Epub 2017 Jun 22.
A SrRhO polytype with six-layered (6M) structure was synthesized under high pressure and high temperature. The crystal structure was obtained by refining X-ray powder diffraction with the monoclinic space group C2/c with lattice parameters a = 5.5650(1) Å, b = 9.5967(2) Å, c = 14.0224(4) Å, and β = 92.846(2)°. It is isostructural with SrIrO synthesized under ambient pressure and consists of dimers of the face-shared Rh(2)O octahedra connected by their vertices to the corner-shared Rh(1)O octahedra along the c axis with a stacking of SrO layers in the sequence of CCHCCH, where C and H denote cubic and hexagonal closed packing, respectively. With increasing pressure, the 6M SrRhO transforms to an orthorhombic perovskite (Pv) phase, having a = 5.5673(1) Å, b = 5.5399(2) Å, c = 7.8550(2) Å in the space group Pbnm. A pressure-temperature phase diagram shows that the 6M-Pv phase boundary moves to lower temperatures with increasing pressure. Both the 6M and the Pv phases of SrRhO were characterized by magnetic susceptibility, resistivity, and thermopower; they are all metals with an enhanced and temperature-dependent magnetic susceptibility; no long-range magnetic order has been found. The polytype structures are normally found in ABO oxides with the geometric tolerance factor t > 1. SrRhO represents another example (in addition to SrIrO) where the polytype 6M structure can be stabilized with a t < 1.
一种具有六层（6M）结构的SrRhO多型体在高压高温下合成。通过用单斜空间群C2/c对X射线粉末衍射进行精修获得晶体结构，晶格参数为a = 5.5650(1) Å，b = 9.5967(2) Å，c = 14.0224(4) Å，β = 92.846(2)°。它与在常压下合成的SrIrO同构，由面共享的Rh(2)O八面体二聚体组成，这些二聚体通过其顶点与沿c轴角共享的Rh(1)O八面体相连，SrO层按CCHCCH顺序堆积，其中C和H分别表示立方和六方密堆积。随着压力增加，6M SrRhO转变为正交钙钛矿（Pv）相，在空间群Pbnm中a = 5.5673(1) Å，b = 5.5399(2) Å，c = 7.8550(2) Å。压力-温度相图表明，随着压力增加，6M-Pv相界向低温移动。SrRhO的6M相和Pv相均通过磁化率、电阻率和热功率进行表征；它们都是具有增强的且与温度相关的磁化率的金属；未发现长程磁有序。多型结构通常出现在几何容忍因子t > 1的ABO氧化物中。SrRhO代表了另一个例子（除SrIrO外），其中多型6M结构在t < 1时可以稳定存在。
