Electrical anomalies and the localized to delocalized transition for lanthanide pnictides at high pressures

利用同步辐射，在室温下研究了具有氯化钠结构的LnBi(Ln=La，Nd，Sm，Gd，Tb，Ho和Tm)的粉末X射线衍射。得到了SmBi的详细压力-体积关系。本尼迪克特等人报道的等结构相变。在2.6 Gpa左右没有发现。然而，我们在18 Gpa附近观察到了SmBi的一级相变。SmBi由NaCl型转变为四方(扭曲的CsCl型)结构，在18 Gpa附近的体积崩塌约为8.2%。SmBi20.3 Gpa高压相的晶胞参数为a=3.775(5)Å，c=3.25(2)Å，c/a=0.86，V=46.4(3)Å^3。高压下SmBi的结构与SMAS的结构是同构的。用Birch状态方程对SmBi的体积-压力曲线进行了拟合，得到了SmBi的体积弹性系数。该化合物的体积弹性模量及其压力导数分别为B_0=67±2 GPA，B_0‘=2.6±0.3。我们还发现了LnBi(Ln=La，Nd，Sm，Gd，Tb，Ho和Tm)在高压下的结构相变。

By use of synchrotron radiation, powder x-ray diffraction of LnBi (Ln = La, Nd, Sm, Gd, Tb, Ho and Tm) with a NaCl-type structure has been studied up to 35 GPa at room temperature. The detailed pressure-volume relationship for SmBi is obtained. The isostructural phase transition reported by Benedict et al. is not found at around 2.6 GPa. However, we have observed a first-order phase transition for SmBi at around 18 GPa. SmBi transforms from the NaCI-type to a tetragonal (distorted CsCl-type) structure with the volume collapse of about 8.2 % at around 18 GPa. Crystal data of the high-pressure phase of SmBi are a = 3.775(5) Å, c = 3.25 (2) Å, c/a = 0.86 and V = 46.4 (3) Å^3 at 20.3 GPa. The structure of SmBi at high pressure is isostructural with that of SmAs. A bulk modulus of SmBi is obtained from the volume vs. pressure curve fitted by a Birch equation of state. The bulk modulus and its pressure derivative of this compound are B_0 = 67 ± 2 GPa, B_0' = 2.6 ± 0.3. We have found also the structural phase transitions for LnBi (Ln = La, Nd, Sm, Gd, Tb, Ho and Tm) at high pressures.