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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >The Low-Temperature Phase Transition Sequence of the Halide Perovskite Tetramethylammonium Trichlorogermanate(II) and the Structure of its Incommensurately Modulated δ-Phase
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The Low-Temperature Phase Transition Sequence of the Halide Perovskite Tetramethylammonium Trichlorogermanate(II) and the Structure of its Incommensurately Modulated δ-Phase

机译：卤化物钙钛矿四甲基三氯锗酸（II）的低温相变序列及其调制度δ相的结构

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摘要

Tetramethylammonium trichlorogermanate(II), N(CH3)4-GeCl3, abbreviated as TGC, has been investigated by temperature-dependent X-ray powder and single-crystal diffraction. It is shown that TGC has a one-dimensional incommensurately modulated phase, called the 5-phase, with primary modulation wavevector q " 0.14 b*. This phase is stable in the temperature range 170 < T < 200 K and occurs between the room-temperature phase y and a lower-temperature phase s. The structure of 5-TGC was refined in the (3+l)-dimensional superspace group Pnam(0fi0)00s. The average structure of 5-TGC with lattice parameters 13.083 (6) x 8.841 (4) x 9.027 (4) A3 (T = 190 K) is isomorphous to the structure of the normal room-temperature phase y. The latter is of distorted perovskite-type [Depmeier, MQller & Klaska (1980). Acta Cryst. B36, 803-807]. The modulation in the case of the 5-phase is purely displacive, the dominant modulation wave being polarized along the c-axis and of magnitude 0.42 A. The low-temperature phase s is monoclinic with lattice parameters 13.068(6) x 8.808(5) x 8.962(6)A3, a = 93.9(1)° at T - 160 K. The intensity of the incommensurate satellite reflections vanishes at the S-s transition. The observed diffraction patterns suggest that the S-s transition at 170 K is also associated with the partial reappearance of the orthorhombic lattice of the y-phase. In fact, both single-crystal and powder diffraction display the super-position of a monoclinic and an orthorhombic reciprocal lattice, which persists from Ts.s = 170 K down to at least 130 K. The intensity ratio of monoclinic to orthorhombic reflections is ca 5:1 and is essentially constant for T < 160 K.
机译：通过与温度相关的X射线粉末和单晶衍射研究了三氯锗酸四甲基铵（II）N（CH3）4-GeCl3（缩写为TGC）。结果表明，TGC具有一维不相称的调制相位，称为5相，其主调制波矢量q“ 0.14 b *。该相位在170

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