Perovskites with Bi or Pb on the A site host a number of interesting and yet to be understood phenomena such as negative thermal expansion in ${\mathrm{BiNiO}}_3$. We employ hard x-ray photoemission spectroscopy of Ni $2p$ core level as well as valence band to probe the electronic structure of ${\mathrm{BiNiO}}_3$ and ${\mathrm{PbNiO}}_3$. The experimental results supported by theoretical calculations using dynamical mean-field theory reveal essentially identical electronic structure of the Ni–O subsystem typical of ${\mathrm{Ni}}^{2+}$ charge-transfer insulators. The two materials are distinguished by filling of the Bi(Pb)–O antibonding states in the vicinity of the Fermi level, which is responsible for the Bi disproportionation in ${\mathrm{BiNiO}}_3$ at ambient pressure and absence of similar behavior in ${\mathrm{PbNiO}}_3$. The present experiments provide evidence for this conclusion by revealing the presence/absence of Bi/Pb $6s$ states at the top of the valence band in the two materials.

中文翻译：

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硬X射线光电子能谱揭示BiNiO3和PbNiO3金属间电荷转移和键歧化机制

A 位上含有 Bi 或 Pb 的钙钛矿存在许多有趣但尚待理解的现象，例如负热膨胀${\mathrm{镍酸铋}}_3$。我们采用 Ni 的硬 X 射线光电子能谱$2p$核心能级和价带来探测电子结构${\mathrm{镍酸铋}}_3$和${\mathrm{镍酸铅}}_3$。使用动态平均场理论的理论计算支持的实验结果揭示了典型的 Ni-O 子系统基本相同的电子结构${你}^{2+}$电荷转移绝缘体。这两种材料的区别在于费米能级附近填充了 Bi(Pb)-O 反键态，这是造成 Bi 歧化的原因。${\mathrm{镍酸铋}}_3$在环境压力下并且没有类似的行为${\mathrm{镍酸铅}}_3$。本实验通过揭示 Bi/Pb 的存在/不存在为这一结论提供了证据$6s$态位于两种材料的价带顶部。