六方亚稳相ReO_(3)的高压合成和调控

Synthesis and High-Pressure Regulation of Hexagonal ReO_(3)

ReO_(3)具有A位缺失的立方钙钛矿结构,在压力下会经历系列结构相变。近期,通过高压低温电阻测试,发现其高压R-I相(空间群为R3^(-)c)具有高达17 K的超导转变温度。为探索新型Re氧化物超导体,采用ReO_(3)为前驱体,在10 GPa和600℃的高压高温条件下制备了具有六方对称性(空间群为P6_(3)22)的亚稳相,并在常压下对其晶体结构、磁性和电输运性质进行了表征。实验发现,六方亚稳相的电阻在常压下250 K附近出现明显异常,温度低至2 K时仍未出现超导现象。高压电阻测试表明:常压下250 K附近ReO_(3)的电阻异常迅速消失,亚稳相表现出典型的金属行为;在62 GPa的高压条件下,温度低至1.5 K时仍未出现超导电性。

ReO_(3) with A-site-vacant perovskite structure undergoes sequential pressure-driven structural transformations.Recently,we found that its high-pressure rhombohedral R-Ⅰphase(space group R3^(-)c)is superconducting with an optimal superconducting transition temperature(T_(c))of 17 K via high-pressure resistance measurements.To explore new superconductors among Re oxides,in this work we prepared a metastable hexagonal phase of ReO_(3)(space group P6_(3)22)by treating the ReO_(3) precursor under 10 GPa and 600℃,and characterized its crystal structure,magnetic and electrical transport properties.The results show that P6_(3)22 phase is not a superconductor down to 2 K at ambient pressure,but displays an anomaly around 250 K in resistivity.High-pressure resistance measurements show that the anomaly at about 250 K in ambient pressure disappears quickly upon compression,and P6_(3)22 phase shows typical metallic behavior in the whole temperature range without showing any signature of superconductivity down to 1.5 K under pressures up to 62 GPa.In the future,comparative theoretical studies of the hexagonal P6_(3)22 phase and the R-Ⅰphase of ReO_(3) will help to understand the mechanism of superconductivity in this system.