Various phases and associated phase transitions between them have been investigated in the complex pseudobinary perovskite solid solutions, $(1-x)Pb (Fe_ \frac{1}{2} Ta_\frac{1}{2}) O_3 -xPb(Mg_\frac{1}{2} W_\frac{1}{2}) O_3$ and $(1-x)Pb(Fe_\frac{1}{2} Nb_\frac{1}{2}) O_3-xPb(Mg_ \frac{1}{2} W_ \frac{1}{2}) O_3$, with dielectric susceptibility, differential scanning calorimeter, and thermal expansion measurement. The apparent antiferroelectric transition temperature decreases linearly with the increase of the solute ferroelectric $Pb(Fe_
\frac{1}{2} Ta_\frac{1}{2}) O_3$ concentration in the high antiferroelectric $Pb(Mg_ \frac{1}{2} W_\frac{1}{2}) O_3$ concentration range. Further increase of $Pb(Fe_ \frac{1}{2} Ta_\frac{1}{2}) O_3$ concentration past x=0.82 no longer decreases the transition temperature linearly and the apparent transition temperature in the mid composition range of the solid solution remains relatively constant with respect to a compositional change. In the high $Pb(Fe_\frac{1}{2} Ta_\frac{1}{2}) O_3$ concentration range, transition temperature decreases linearly with the increase of $Pb(Mg_\frac{1}{2} W_\frac{1}{2}) O_3$ until x=0.2 is reached. This transition behavior is in good agreement with the so called GLP (glass like phase) random bond model or the phase diagram of $Rb_{1-x}(NH_4)_x H_2PO_4$ which hints that the low temperature phase in the mid composition range is possibly the dipole glass phase. Using this observation and the concept of percolation and proposed block Hamiltonian, the author shows that the normal antiferroelectric or ferroelectric phase does not appear for 0.200.86, but it decrease for x<0.82. All these phenomena are positive evidence for the possible dipole glass phase formation in the mid composition range. $(1-x)Pb (Fe_\frac{1}{2}Nb_\frac{1}{2}) O_3-xPb(Mg_ \frac{1}{2} W_\frac{1}{2})O_3$ system behaves almost identically with the $(1-x)Pb(Fe_\frac{1}{2}Ta_\frac{1}{2})O_3-xPb(Mg_\frac{1}{2}W_ \frac{1}{2})O_3$ system and all the concepts developed for $(1-x)Pb(Fe_ \frac{1}{2} Ta_\frac{1}{2})O_3 -xPb (Mg_\frac{1}{2} W_\frac{1}{2})O_3$ are equally applied to this system. The specific heat and thermal expansion data are also reported in these two systems in order to study the origin of the diffuse transition. This study is done mainly on the antiferroelectric composition range. The specific heat data reveal that even the transition of the pure $Pb(Mg_\frac{1}{2} W_\frac{1}{2})O_3$ is smeared. The thermal expansion results reveal hidden details of the phase transition characteristics of the dielectric constant data. In particular, they display a temperature range in which the thermal expansion coefficient becomes virtually zero. This temperture range lies just above the antiferroelectric transition temperature region. With this result, the irreversible and the reversible dipole region are separated in the diffuse phase transition range. The possible origin of the dispersion of the dielectric peak temperature is also explained by using the concept of the relaxation.
페롭스카이트 고용체 $(1-x)P_b(F_{e\frac{1}{2}}T_{a\frac{1}{2}})O_3-x P_b(M_{g\frac{1}{2}} W_{\frac{1}{2}}) O_3$ 및 $(1-x)P_b (F_{e\frac{1}{2}} N_{b\frac{1}{2}}) O_3-xP_b(M_{g\frac{1}{2}} W_{\frac{1}{2}})O_3$ 계에서 유전 특성과 열분석실험을 하여 확산된 상전이및 쌍극자 유리현상에 대해서 연구하였다. 확산된 상전이 현상에 대한 연구부분에서는 주로 열팽창 및 유전상수 측정을 하여 지금까지 상충 되어왔던 두가지의 이론적 모형, 즉 Compositional fluctuation 및 local disorder 모형이 하나의 계에서 동시에 존재할 수 있음을 보여주었다. 쌍극자 유리현상에 대한 연구부분에서는 block Hamiltonian 및 percolation의 개념과 상전이 온도의 조성 의존성에 대한 실험결과등을 통해서 페롭스카이트 강유전체와 반강유전체의 혼합물에서도, 다른 경우와 마찬가지로 중간 조성 영역에서 쌍극자 유리가 존재한다는 것을 보여주었다. 유전상수의 최고 점온도의 주파수 의존성에 대한 연구부분에서는 Compositional fluctuation 개념을 사용하여 측정주파수가 고주파일수록 유전상수의 최고점 온도가 높다는 것을 설명하였다.