Structural Change Associated with the Structural Phase Transition

结构相变的特征是原子的位移或原子团的取向变化。因此，研究过渡点上下的晶体结构是非常重要的。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，安装在四圆衍射仪上，以测量高温下的布拉格反射。2)得出了硫酸甘氨酸晶体的电偶极矩的大小与温度有关的结论。这一结果需要考虑这一新发现的性质来构造结构相变的真实图像。3)通过确定原子势函数的系数来研究SrTi&lt；O_3&gt；结果表明，随着相变温度的接近，二次项变小，从而从结构上理解了晶格不稳定性。4)目前正在进行以下研究：研究&lt；LiH_3&gt；&lt；(SeO_3)_2&gt；的熔化机理，研究DLP晶体的无序结构，研究氢键晶体&lt；KH_2&gt；&lt；PO_4&gt；，(&lt；NH_4&gt；)&lt；H_2&gt；&lt；PO4&gt；和&lt；KH_3&gt；(SeO_3)&gt；&lt；&lt；2&gt；等一系列研究的完成，将有助于加深对结构相变机理的理解。

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.