Abstract The single-crystal structures of YbB12, TmB12, and LuB12 were studied in the temperature range of 88–293 K, those of HoB12 and ErB12 – in the range of 88–500 K using high-resolution X-ray diffraction data in order to correlate the structure changes with the changes in the physical properties of the dodecaborides under study. The lattice deformations caused by the cooperative Jahn – Teller effect were studied. A method is proposed for approximating the temperature dependences of atomic displacement parameters (ADPs) from lattice sites using the extended Debye or Einstein models. The break points in the temperature dependences of ADPs in combination with nonmonotonic changes in the lattice parameters near the critical temperatures Tc indicate phase transformations revealed from diffraction data. The lattice instability and the rearrangement of the phonon spectrum near Tc are accompanied by the observed changes in the physical characteristics. A sensitive structural diagnostic tool was created to detect implicit phase transitions, quantum critical points and quantum instabilities of various nature that lead to the appearance of anomalies in the physical properties of crystals.

中文翻译：

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稀土十二硼化物 RB12 (R=Ho-Lu) 在中等温度下的结构不稳定性和定义不明确的相变

摘要 利用高分辨率 X 射线衍射数据依次研究了 YbB12、TmB12 和 LuB12 在 88-293 K 温度范围内的单晶结构，以及 HoB12 和 ErB12-88-500 K 温度范围内的单晶结构。将结构变化与所研究的十二硼化物物理性质的变化联系起来。研究了由合作的 Jahn-Teller 效应引起的晶格变形。提出了一种方法，用于使用扩展的德拜或爱因斯坦模型从晶格位置逼近原子位移参数 (ADP) 的温度依赖性。ADP 温度依赖性的断点与临界温度 Tc 附近晶格参数的非单调变化相结合，表明衍射数据揭示了相变。晶格不稳定性和 Tc 附近声子谱的重排伴随着观察到的物理特性的变化。创建了一种灵敏的结构诊断工具，以检测导致晶体物理性质出现异常的各种性质的隐式相变、量子临界点和量子不稳定性。