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<p>The mixed nature of the ferroelectric phase transition in potassium dihydrogen phosphate (KDP), involving both a displacive component associated with the distortion of PO<sub>4</sub> ions and an order–disorder component arising from H-atom disorder in O–H–O′ hydrogen bonds, was investigated using Raman scattering spectroscopy. By analyzing the subtle changes in the Raman frequencies of the crystal in the temperature range Tc&#xa0;&lt;&#xa0;T&#xa0;&lt;&#xa0;173&#xa0;K, it is argued that, prior to undergoing the ferroelectric phase transition at Tc, the crystal passes through a pretransitional phase within the temperature range Tc&#xa0;&lt;&#xa0;T&#xa0;&lt;&#xa0;173&#xa0;K. In this pretransitional phase, a large number of micropolar regions begin to form within the crystal owing to the dipolar distortion of PO<sub>4</sub> ions induced by the oscillating electric field generated by disordered H atoms. As the temperature approaches Tc, the size of these micropolar regions increases, and at Tc the crystal finally becomes polar.</p>

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Raman investigation of pretransition behaviour in potassium dihydrogen phosphate crystals and study of coupling between the PO4 distortion and hydrogen atom disorder in these crystals

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • R R Choudhury,
  • R Chitra,
  • S Kesari,
  • R Rao

摘要

The mixed nature of the ferroelectric phase transition in potassium dihydrogen phosphate (KDP), involving both a displacive component associated with the distortion of PO4 ions and an order–disorder component arising from H-atom disorder in O–H–O′ hydrogen bonds, was investigated using Raman scattering spectroscopy. By analyzing the subtle changes in the Raman frequencies of the crystal in the temperature range Tc < T < 173 K, it is argued that, prior to undergoing the ferroelectric phase transition at Tc, the crystal passes through a pretransitional phase within the temperature range Tc < T < 173 K. In this pretransitional phase, a large number of micropolar regions begin to form within the crystal owing to the dipolar distortion of PO4 ions induced by the oscillating electric field generated by disordered H atoms. As the temperature approaches Tc, the size of these micropolar regions increases, and at Tc the crystal finally becomes polar.