An original approach for the determination of unit cell parameter temperature dependence using a conventional single-crystal X-ray diffractometer is proposed. The approach is based on the calibration of the goniometer equatorial circle segment using the position of several Kα₁/Kα₂ doublets from reference single crystals. It allows for the refinement of lattice parameters of single crystals with a relative error of less than 10⁻⁴. Its capabilities are demonstrated using an example of tetragonal single crystals. The space group, crystal structure, and composition of t-Ag_0.8Li_0.2InSe₂ were determined using single-crystal X-ray diffraction analysis of three small (linear sizes ∼0.1 mm) fragments from a larger (linear sizes up to 10 mm) single-crystal grown using the Bridgman method. The dynamics of the crystal structure changes in the temperature range of 90–500 K were studied. The obvious anisotropy of t-Ag_0.8Li_0.2InSe₂ thermal behavior was shown with an overall increase in the volume of the tetragonal unit cell by 0.51%—parameter a increased by 0.34, while parameter c decreased by 0.17%. The nonlinear dependence of the thermal expansion tensor elements on temperature was determined: α₁₁ × 10⁶ = −4.28 + 0.08T − 1.95 × 10⁻⁴T² and α₃₃ × 10⁶ = −5.59 + 0.01T − 1.97 × 10⁻⁵T².

中文翻译：

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以 t-Ag0.8Li0.2InSe2 为例，开发了一种精确测定单晶热应变张量元素的方法

提出了一种使用传统单晶 X 射线衍射仪确定晶胞参数温度依赖性的原始方法。该方法基于使用来自参考单晶的多个 Kα ₁ /Kα ₂双峰的位置对测角仪赤道圆段进行校准。它可以细化单晶的晶格参数，相对误差小于10 ^-4。它的功能通过四方单晶的例子得到了证明。 t-Ag _0.8 Li _0.2 InSe ₂的空间群、晶体结构和成分是通过对来自较大（线性尺寸高达 10 mm）的三个小（线性尺寸~0.1 mm）碎片进行单晶 X 射线衍射分析来确定的。 ）使用布里奇曼法生长单晶。研究了90-500 K温度范围内晶体结构变化的动力学。 t-Ag _0.8 Li _0.2 InSe ₂热行为表现出明显的各向异性，四方晶胞体积总体增加了0.51%，参数a增加了0.34，而参数c减少了0.17%。确定热膨胀张量元素对温度的非线性依赖性：α ₁₁ × 10 ⁶ = -4.28 + 0.08 T - 1.95 × 10 ^-4 T ²和α ₃₃ × 10 ⁶ = -5.59 + 0.01 T - 1.97 × 10 ^{- 5} T ²。