Pressure-induced delocalization in charge-ordering rare-earth compounds studied bynuclear resonant scattering

的压力与温度的相图的混合价Eu 4As 3化合物的测定通过使用同步辐射的X-射线衍射测量。在常压下，随着体积的减小，结构相变发生在343 K，转变温度随压力线性增加，直到约5 GPa。根据克劳修斯-克拉珀龙关系式，这个转变的熵变估计为41 J/molK。该值比Eu^<3+>和Eu^<2+>离子在Eu_4As_3的热价涨落态中的随机排列所预期的组态熵大一倍。<151>在301 - 406 K温度范围内，对Eu_4As_3进行了核共振非弹性X射线散射（NRIXS）实验。我们推导出的热力学参数，从非弹性成分中观察到的NRIXS光谱使用求和规则。平均无反冲分数表明Eu离子在B边界附近的晶格振动软化 ...更多信息 在价态涨落状态下的Rillouin区。通过平均力常数的温度依赖性，我们提出Eu_4As_3中4f态与导带或价带的杂化在电荷有序温度附近和价涨落态中起作用。并从衍射数据中精确地导出了单个原子坐标以及晶格参数。我们已经证实，与R3 c空间群的三角结构不改变高达19 GPa。在10 GPa的变形角的压力依赖性的变化，虽然体积显示没有异常的压力的函数。结果表明，EuAs_6八面体的体积与Eu离子的价态密切相关，在常压下处于电荷有序态时，纯的三价和二价Eu离子分别占据两个不等价的Eu位.我们提出了明确的证据的基础上的压力依赖性的这些体积在两个不等价的Eu网站的静电荷秩序的熔化发生在10 GPa和Eu_4As_3是在一个混合价态以上10 GPa。少

The pressure versus temperature phase diagram of the mixed-valent Eu4As3 compound was determined by means of x-ray diffraction measurements using synchrotron radiation. The structural phase transition occurs at 343 K under ambient pressure with volume reduction and the transition temperature increases linearly with pressure up to about 5 GPa. The entropy change at this transition is estimated to be 41 J/molK from the Clausius-Clapeyron relation. The value is twice lager than the configuration entropy which is expected from the random arrangement of Eu^<3+> and Eu^<2+> ions in the thermally derived valence fluctuating state of Eu_4As_3.^<151>Eu nuclear resonant inelastic x-ray scattering (NRIXS) experiments have been performed on Eu_4As_3 from 301 to 406 K. We derived the thermodynamic parameters from inelastic components in the observed NRIXS spectra using the sum rules. The mean recoilless fraction shows the softening in the lattice vibration of the Eu ion around the boundary of the B … More rillouin zone in the valence fluctuating state. We present by the temperature dependence of mean force constant that the hybridization between the 4fstates and the conduction or valence bands in Eu_4As_3 plays a role around the charge ordering temperature and in the valence fluctuating state.We have carried out high-pressure x-ray diffraction experiments on Eu_4As_3 at mom temperature, and individual atomic coordinates as well as lattice parameters were derived precisely from the diffraction data. We have confirmed that a trigonal structure with the R3c space group does not change up to 19 GPa. The pressure dependence of the distortion angle changes at 10 GPa although the volume shows no anomaly as a function of pressure. The results show that the volume of the EuAs_6 octahedron and the valence state of the Eu ion are closely correlated, and pure trivalent and divalent Eu ions occupy two nonequivalent Eu sites, respectively, in the charge-ordered state at ambient pressure. We present dear evidence on the basis of the pressure dependence of these volumes at two nonequivalent Eu sites that a melting of the static charge order occurs at 10 GPa and Eu_4As_3 is in a mixed-valence state above 10 GPa. Less