Solid Solution Single Crystals Research Articles

Study of Ferroelectric Transitions of Solid-Solution Single Crystals of KNbO3-KTaO3

Methods of preparation and results of measurements of the dielectric constant of solid-solution single crystals of KNb${\mathrm{O}}_{3}$ and KTa${\mathrm{O}}_{3}$ are presented. Data are given for the composition range 0-80 mole percent KTa${\mathrm{O}}_{3}$ in the temperature interval -180\ifmmode^\circ\else\textdegree\fi{}C to 450\ifmmode^\circ\else\textdegree\fi{}C. It is found that all of the crystals studied show Curie-law behavior of the dielectric constant in the paraelectric state. The data indicate that the paraelectric to ferroelectric transition, which is first order for pure KNb${\mathrm{O}}_{3}$, becomes second order at a concentration of approximately 55 mole percent KTa${\mathrm{O}}_{3}$. Analysis of the results in terms of Slater's model of ferroelectricity in a perovskite lattice leads to the conclusion that the dependence of the Lorentz correction on volume plays a major role in determining the ferroelectric behavior. Ionic polarizabilities and their dependence on volume are also discussed.

X-ray Studies on the Structures of Solid Solutions NaCl-CaCl2 I. Main Results and General Considerations

Stationary X-ray diffraction patterns from transparent single crystals of solid solutions of NaCl dissolved with a few per cent of CaCl 2 show a number of diffuse spots. Their displacements with the change of the direction of incident X-rays reveal the existence of several kinds of rods in reciprocal space. Among them, the rods running along and rows are most remarkable. The appearance of these rods are considered as the result of the formation of thin plate-like precipitates in the matrix because of the homogeneous solid solutions being unstable at room temperatures. The precipitates may be the places where Ca ++ ions replacing Na + ions, and vacancies of Na + sites, are locally concentrated. It was shown, by a general consideration, that the plate-like precipitate responsible for or rods is likely composed of an assembly of anti-phase, domains of super structures.