Phase Transformation Seen Through"Millikelvin-Stabilized Cell"―Detection by X-ray Diffraction―

A Simple and versatile“millikelvin-stabilized cell”has been developed to investigate phase transformation stage in solid precisely。It can be used as a fine DC calorimeter and also，by mounting on a goniometer head，as an X-ray diffraction cell with a function of sensing thermal anomaly.When applied to the well knownown 320K phase transformation in CsPbCl锡D23锡D2，it was found that it occurs not in a single-stage but in a hyperfine multistage in the temperature range of approximately 0.1K.The results required a reinterpretation of the mechanism on the successive phase transition of the crystal.In order to make clear the hyperfine multistage transition，we have reexamined the phase changes of the crystal over wide temperature range，340K-90K，by means of single crystal X-ray photographic method。On cooling from room temperature，it was found that about265K，an abrupt increase of intensity was observed at0k1+1/2superlattice reflections corresponding to the X-point in the cu…More bic Brilloun zone.With lowering temperature further to 200K，another abrupt increase of intensity was observed at h+1/2k+1/2 1+1/2superlattice reflections which correspond to the R-point.The anomaly at the 200K，although accompanies with conspicuous splitting of the h k1Bragg spots along[010]c*direction，weak spots without splitting were still observed.These facts indicated that a coexistence of two crystal forms exists in the lowest temperature phase below 200K.One is a monoclinic form and the other is tetragonal one.The results in this study suggests that the crystal undergoes two series of successive structural changes starting from the superfine anomalies at the 320K transition。One is 320-315-310K transition series(series“II”)which is related to the so called soft phonon condensation theory，and the other is 320-265-200K transition series，series“I”，which is however dominant in the specimen.The 408K phase transformation in BaTier D23西耶D2 by means of“millikelvin-stabilized cell”was also revealed to occur in multistage.An anomalous transition was also detected in(KCN)x(KBr)I D21-x D 2 mixed crystal in advance study on the phase transition.Application of the“millikelvin-stabilized cell”to the precise study on the phase transition is now planned on these crystals.Less：Less

A Simple and versatile"millikelvin-stabilized cell" has been developed to investigate phase transformation stage in solid precisely. It can be used as a fine DC calorimeter and also, by mounting on a goniometer head, as an X-ray diffraction cell with a function of sensing thermal anomaly. When applied to the well known 320 K phase transformation in CsPbClィイD23ィエD2, it was found that it occurs not in a single-stage but in a hyperfine multistage in the temperature range of approximately 0.1 K.The results required a reinterpretation of the mechanism on the successive phase transition of the crystal. In order to make clear the hyperfine multistage transition, we have reexamined the phase changes of the crystal over wide temperature range, 340 K-90 K, by means of single crystal X-ray photographic method. On cooling from room temperature, it was found that at about 265K, an abrupt increase of intensity was observed at 0 k 1+ 1/2 superlattice reflections corresponding to the X-point in the cu … More bic Brilloun zone. With lowering temperature further to 200 K, another abrupt increase of intensity was observed at h+1/2 k+1/2 1+1/2 superlattice reflections which correspond to the R-point. The anomaly at the 200K, although accompanies with conspicuous splitting of the h k 1Bragg spots along [010]c* direction, weak spots without splitting were still observed. These facts indicated that a coexistence of two crystal forms exists in the lowest temperature phase below 200 K. One is a monoclinic form and the other is tetragonal one. The results in this study suggests that the crystal undergoes two series of successive structural changes starting from the superfine anomalies at the 320 K transition. One is 320―315―310 K transition series (series" II") which is related to the so called soft phonon condensation theory, and the other is 320―265―200 K transition series, series "I", which is however dominant in the specimen.The 408 K phase transformation in BaTiOィイD23ィエD2 by means of "millikelvin-stabilized cell" was also revealed to occur in multistage. An anomalous transition was also detected in (KCN)x(KBr) ィイD21-xィエD2 mixed crystal in advance study on the phase transition. Application of the "millikelvin-stabilized cell" to the precise study on the phase transition is now planned on these crystals. Less