Structural Change Associated with the Structural Phase Transition

结构相变的特征是原子位移或原子群的取向变化。因此，研究过渡点上下的晶体结构是很重要的。沿着这条线，我们研究了以下化合物的结构变化。1)首先，我们制作了一个低温恒温器，将其设置在四圆衍射仪上，以测量高温下的布拉格反射。2)硫酸甘油三酯晶体电偶极矩的大小与温度有关。这一结果要求考虑这一新发现的性质来构建结构相变的真实图景。3)通过测定原子势函数系数，研究了SrTi <O_3>。结果表明，随着转变温度的接近，二次项变小，从而从结构的角度理解晶格不稳定性。计算是由一台个人计算机进行的，这台计算机是由援助款提供的。4)以下调查正在进行中；即研究了<LiH_3> <(SeO_3)_2>的熔融机理，研究了DLP晶体的无序结构，研究了<KH_2> <PO_4>, (<NH_4>) <H_2> <PO_4>和<KH_3> <(SeO_3)> <_2>的氢键晶体转变机理。通过一系列的研究，我们将有助于对结构相变机理的深入理解。

The structural phase transition is characterized by the atomic displacement or the orientational change of the atomic group. Therefore, it is important to investigate the crystal structure above and below the transition point. Along this line, we studied the structural change of following compounds.1) At first, we made a cryostat, which was set on a four-circle diffractometer, in order to measure Bragg reflections at high temperatures.2) It is concluded that the magnitude of the electric dipole moment of triglycine sulfate crystals depends on the temperature. This result requires to consider this newly found nature to construct the real picture of the structural phase transitition.3) SrTi <O_3> was investigated by determining the coefficients of the atomic potential function. It turns out that the quadratic term becomes small with approaching the transition temperature leading to the understanding of lattice instability from the structural viewpoint. The calculation was carried out by a personal computer which was taken by the grant-in-aid.4) Following investigations are now in progress; i.e. the study of the melting mechanism of <LiH_3> <(SeO_3)_2> , the study of the disordered structure of DLP crystals and the study of the transition mechanism of the hydrogen bonded crystals <KH_2> <PO_4> , ( <NH_4> ) <H_2> <PO_4> and <KH_3> <(SeO_3)> <_2> .We will contribute to get deeper understanding of the mechanism of the structural phase transition by completing a series of these studies.