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Establishment of the New Viewpoint on the Dynamical Mechanism of Structural Phase Transitions in Hydrogen-bonded Crystals

氢键晶体结构相变动力学机制新观点的建立

基本信息

批准号：
02302021
负责人：
TOKUNAGA Masaharu
金额：
$ 7.49万
依托单位：
(Faculty of Science) Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Co-operative Research (A)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1992
项目状态：
已结题

项目摘要

(1) A long controversy had been held between the proton tunneling model (traditional) and the H_2PO_4 order-disorder model (the new viewpoint presented by us) with respect to the dynamical mechanism of structural phase transition in KH_2PO_4, which is a representative of hydrogen-bonded crystals. The existence of tunneling motions of protons has been proved to be excluded by the experimental results of incoherent neutron scattering.(2) The Raman spectra of KH_2PO_4 observed and interpreted by Kaminow-Damen and Peercy had been long regarded as the evidence of the former model. New precise experimental data in Raman scattering, hyper-Raman scattering, and far infrared reflection have been obtained on KH_2PO_4, KD_2PO_4 and their isomorphous crystals in wide temperature region and under high pressure. These data have been successfully analysed in terms of the critical relaxation mode and the lowering of the local symmetry of PO_4 radicals due to the disordered structure above the transition temperature.From both results, the new viewpoint has been concluded to hold as far as KH_2PO_4 type crystals are concerned. This viewpoint will be extended to all hydrogen-bonded crystals.(3) Phase transitions in zero-dimensional hydrogen-bonded systems M_3H(XO_4)_2 (M=K, Rb, Cs ; X= S, Se) have been found and studied by crystallographical, calorimentrical and optical methods. The origin of the large isotope effect due to the substitution of H by D has been attributed to the difference in geometrical configurations of atoms in the H(XO_4)_2 radical including that of electron densityon the hydrogen bond.(4) Several new phases and variations of transition temperatures have been found by subsituting H by D and under high pressure in some hydrogen-bonded crystals.

(1)关于氢键晶体KH_2PO_4结构相变的动力学机制，质子隧穿模型(传统模型)和H_2PO_4有序-无序模型(我们提出的新观点)之间的争论由来已久。非相干中子散射的实验结果已经证明了质子隧穿运动的存在。(2)Kaminow-Damen和Peercy观测和解释的KH_2PO_4的拉曼光谱一直被认为是前一个模型的证据。在宽温区高压条件下，获得了KH_2PO_4、KD_2PO_4及其同构晶体的喇曼散射、超拉曼散射和远红外反射的新的精确实验数据。从临界弛豫模和转变温度以上无序结构引起的PO4自由基局域对称性的降低两个方面成功地分析了这些数据，由此得出新的观点对于KH_2PO_4型晶体是成立的。这一观点将推广到所有氢键晶体。(3)用结晶学、热重和光学方法研究了零维氢键体系M_3H(XO_4)_2(M=K，Rb，Cs；X=S，Se)的相变。由于H(XO_4)_2自由基中原子几何构型的不同，包括氢键上的电子密度的不同，D取代H产生了大的同位素效应。(4)在某些氢键晶体中，用D取代H发现了几个新的相和转变温度的变化。