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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Structures of room-temperature and ferroelectric (35 K) phases of deuterated betaine calcium chloride dihydrate
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Structures of room-temperature and ferroelectric (35 K) phases of deuterated betaine calcium chloride dihydrate

机译：氘代甜菜碱二水合氯化钙的室温和铁电（35 K）相的结构

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摘要

The structures of the room-temperature and the lowest-temperature ferroelectric phases of fully deuterated betaine (trimethylammonioacetate) calcium chloride dihydrate have been determined by means of elastic neutron diffraction. In previous structural studies the structural distortions of the incommensurate phase at 130K and the fourfold phase at 90 K were analyzed in terms of symmetry modes. The same approach has been applied in the present case and, as a result, a quantitative comparison of the distortions at different temperatures can be performed. This shows that the A3 (for q ≠ 0) and B2u (for q = 0) modes, corresponding to the order parameter, are predominant for the three phases. In addition, it has been found that the structure of this primary mode remains essentially unaltered in the three phases. There is only an increase in its global amplitude as the temperature decreases. Accordingly, it can be expected that the structures of the remaining intermediate modulated phases in the transition sequence are similar to that of the first incommensurate phase, except for the change of wavevector values and greater amplitude of the distortion. Crystal data: (CD3)3NCD2COOCaCl2.2D2O, MT = 279.0, X = 0.8308 A, Z = 4, F(000) = 552. At room temperature: Prnna, a = 10.95(1), ft = 10.15(1), c = 10.82(1)A, V=1203(2) A3, Dx = 1.54gcm~3, μ = 0.10cm-1, final R = 0.048 for 748 unique observed reflections. At 35 K: Pnlxa, a =10.905(9), 6 = 10.00(1), c= 10.80(1)A, y=1178(2)A3, Dx = 1.57gem-3, μ = 0.11 cm"1, final R = 0.042 for 1726 unique observed reflections.
机译：完全氘化的甜菜碱（三甲基氨乙酸）三水合氯化钙的室温和最低温度铁电相的结构已经通过弹性中子衍射法确定。在先前的结构研究中，根据对称模式分析了130K时不相称相和90K时四重相的结构畸变。在当前情况下已采用了相同的方法，因此，可以对不同温度下的变形进行定量比较。这表明与阶跃参数相对应的A3（对于q≠0）和B2u（对于q = 0）模式在三相中占主导地位。另外，已经发现，该主要模式的结构在三个阶段中基本上保持不变。随着温度降低，其整体振幅只会增加。因此，可以预期的是，除了波矢值的变化和更大的失真幅度外，过渡序列中其余中间调制相位的结构与第一不相称相位的结构相似。晶体数据：（CD3）3NCD2COOCaCl2.2D2O，MT = 279.0，X = 0.8308 A，Z = 4，F（000）= 552.在室温下：Prnna，a = 10.95（1），ft = 10.15（1）， c = 10.82（1）A，V = 1203（2）A3，Dx = 1.54gcm〜3，μ= 0.10cm-1，748次观察到的最终R = 0.048。在35 K：Pnlxa，a = 10.905（9），6 = 10.00（1），c = 10.80（1）A，y = 1178（2）A3，Dx = 1.57gem-3，μ= 0.11 cm“ 1，对于1726次观察到的唯一反射，最终R = 0.042。

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