Experimental and Theoretical Investigation on the Relative Stability of the PdS₂- and Pyrite-Type Structures of PdSe₂

Under ambient condition PdSe2 has the PdS2-type structure. The crystal structure of PdSe2 under pressure (up to 30 GPa) was investigated at room temperature by X-ray diffraction in an energy-dispersive configuration using a diamond anvil cell with a mixture of water/ethanol/methanol as a pressure transmitting medium. A reversible structural transition from the PdS2-type to the pyrite-type structure occurs around 10 GPa, and the applied pressure reduces the spacing between adjacent 2/∝[PdSe2] layers of the PdS2-type structure to form the three-dimensional lattice of the pyrite-type structure. First principles and extended Hückel electronic band structure calculations were carried out to confirm the observed pressure-induced structural changes. We also examined why the isoelectronic analogues NiSe2 and PtSe2 adopt structures different from the PdS2-type structure on the basis of qualitative electronic structure considerations.在常温常压条件下，二硒化钯（PdSe₂）具有二硫化钯（PdS₂）型晶体结构。本研究采用以水/乙醇/甲醇混合液作为传压介质的金刚石对顶砧（diamond anvil cell）装置，通过能量色散X射线衍射（energy-dispersive X-ray diffraction）技术，在室温下对最高压力达30 GPa的二硒化钯晶体结构进行了研究。在约10 GPa的压力下，二硒化钯发生了从二硫化钯型到黄铁矿型（pyrite-type）结构的可逆结构相变；外加压力会压缩二硫化钯型结构中相邻二维[PdSe₂]层的层间距，进而形成黄铁矿型结构的三维晶格。本研究通过第一性原理（First principles）与扩展休克尔（extended Hückel）电子能带结构计算，验证了实验观测到的压力诱导结构相变过程。此外，本研究基于定性电子结构分析，探讨了等电子类似物（isoelectronic analogues）二硒化镍（NiSe₂）与二硒化铂（PtSe₂）为何不具备二硫化钯型晶体结构的原因。