Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. III. The Dipole‐Diluted and Mixed Alkali Cyanide Systems

The elastic dipole model and results presented in two previous papers are applied to study the phase transitions of mixed and diluted alkali cyanide systems. The effect of impurities in the crystal on the phase transition temperature is analyzed at first. It is supposed that part of the CN⁻ ions may be preferentially aligned in some directions and can not rotate freely due to the elastic interaction between CN⁻ ions and impurites. When the concentration of CN⁻ ions, taking part in the ordering process, is less than that corresponding to the suddenly changed amount of order parameter at the phase transition point, the maximum ordering energy in the lattice will not be large enough to permit the ordering process to take place, and the crystal will remain in a disordered state at all temperatures. With this model the experimental results obtained in these systems can be explained reasonably well. The effects of hydrostatic pressure on the phase transition temperature are attempted to be analysed too.