New X‐ray diffraction studies on the crystal structure of ferroelectric [4‐NH₂C₅H₄NH][SbCl₄] indicate that in the broad temperature range from 240 to 304 K covering the three intermediate phases, the crystal structure is modulated. Phase II is incommensurately modulated with modulation vector q = βb*, β varying from 0.60 to 0.66 and monoclinic C2/c(0β0)s0 superspace group. Ferroelectric phase III is commensurate with q = b* and Cc(0β0)0 symmetry. Polar phase IV is incommensurately modulated with β varying from 0.66 to 0.70 and Cc(0β0)0 superspace group. In all phases only first‐order satellites are observed along the b* direction. Two types of periodic deformation are present in the structure of modulated phases. The 4‐aminopyridinium cations are subjected to occupation modulation whereas [SbCl₄]⁻_n chains are displacively modulated. The paraelectric–ferroelectric phase transition is an example of the incommensurate–commensurate transition of the lock‐in type. A new mechanism for this transformation is proposed.

中文翻译：

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再谈铁电4-氨基吡啶四氯锑酸（III）的相变。

对铁电[4-NH ₂ C ₅ H ₄ NH] [SbCl ₄ ]的晶体结构的新X射线衍射研究表明，在涵盖三个中间相的240至304 K的宽温度范围内，晶体结构受到调制。用调制向量q = βb *，β在0.60到0.66之间变化以及单斜C 2 / c（0β0）s 0超空间群，对II相进行无比调制。铁电相III与q = b *和Cc（0β0）0对称性相对应。极性相IV的β值从0.66到0.70不等地调制，并且Cc（0β0）0超空间组。在所有阶段中，沿b *方向仅观察到一阶卫星。调制相位的结构中存在两种类型的周期性变形。4-氨基吡啶阳离子经受职业调制而[的SbCl ₄ ] ^- _ñ链displacively调制。顺电-铁电相变是锁定型不相称-相称转变的一个例子。提出了这种转变的新机制。