Distortion of Local Order Parameter Caused by Impurities in Displacive Phase Transition

Kazuya SAITO

Effects of impurities on structural phase transition of displacive type was examined through molecular dynamics simulation. Anharmonic oscillators were arranged on a two-dimensional square lattice with harmonic nearest-neighbor interaction. Local order parameters were calculated with impurities of different strength. Weak impurities affect more strongly than strong inpurities in relative magnitude.
(J. Phys. Soc. Jpn., 67, 3137-3140 (1998))

Disappearance of Displacive Phase Transition in Crystalline Biphenyl by a Small Amount of Impurity

Yasuhisa YAMAMURA, Kazuya SAITO, Michio SORAI and Isao IKEMOTO

Effects of an impurity on a displacive phase transition are examined for crystalline biphenyl (BP) by adiabatic calorimetry. While the anomaly in the heat capacity remained unchanged by 1 % of naphthalene (NA), the anomaly disappeared at 1 % of 4,4'-difluorobiphenyl (DFBP). The observed effect is discussed in relation to the localization of the soft-mode. Two impurities differ in the existence/absence of the twisting degree of freedom that produces the soft-mode. The DFBP molecule weakly localizes the lattice vivration of BP crystal over the wide range of distance. The localization by the NA molecule is strong and only the close neighboring BP molecules are affected.
(J. Phys. Soc. Jpn., 67, 1649-1654 (1998))

Large Impurity Effect on Phase Behavior of a Molecular Crystal: Heat Capacity of High Purity Bis(4-fluorophenyl)methanone

Kazuya SAITO, Syugo Huzisawa and Isao IKEMOTO

Heat capacity of bis(4-fluorophenyl)methanone was measured for two samples of different quality by adiabatic calorimetry from 8 K to 303 K. Some heat capacity anomalies were detected around 110, 80 and 50 K. A small amount of impurity undetectable by gas-liquid chromatography drastically affects thermal behavior not only in the temperature and shape of thermal anomaly, but also appearance/absence of phases. A possible phase relation is proposed and some thermodynamic quantities are tabulated.
(J. Phys. Chem. Solids, 59, 159-166 (1998))

See also Impurity effect on an Order-Disorder Transition

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