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

Abstract

629 phys. stat. sol. (b) 159, 629 (1990) 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 impurities. When the concentration of CNions, 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.Le modele du dipBle tlastique et les resultats prtsentes dans les deux precedents articles sont utilists dans l'etude de la transition de phase des cyanures d'alcalins mixtes et dilues. L'effet des impuretes du cristal sur la temperature de la transition de phase est analyse en premier. I1 est suppose qu'une part des ions CN-peuvent dtre alignes preferentielement dans certaines directions et ne peuvent pas tournes librement a cause de I'interaction 6lastique entre les ions CN-et les impuretes. Quand la concentration en ions CN-, prenant part au processus de rearrangement, est plus faible que celle correspondant au soudain changement du parametre d'ordre a la transition de phase, l'energie maximum de rearrangement dans le reseau ne sera pas assez importante pour permettre au processus de rearrangement de prendre place, et le cristal restera dans un &tat de desordre a haute temperature. Avec ce modele les resultats experimentaux obtenus pour ce systeme s'expliquent plut8t bien. Nous tentons d'analyser les effets de la pression hydrostatique sur la temperature de la transition de phase. ') Nanjing, People's Republic of China. ' ) 07738 Mexico D.F., Mexico. 3, Salt Lake City, UT 84112, USA. 4, Parts I and I1 see phys. stat. sol. (b) 154, 167 and (b) 154, 181 (1989). 41 physicd (b) 159/2 41'

Dielectric Studies of CN- Dipolar Reorientation and Order-Disorder Behavior in RbCN1-x:KCNx and KCN1-x:NaCNx

“…For KCN x : RbCN 1--x transition to an elastically ordered phase is observed throughout the whole mixture. Several theoretically approaches [9][10][11], including molecular dynamics simulations [12,13] were developed, and various experimental techniques were employed, such as: specific-heat [14,15], ultrasound-velocity [16][17][18], neutron diffraction [19][20][21][22], X-ray diffraction [23], nuclear magnetic resonance [24,25], etc. 11 x 0.84) for which an orientational glassy state is formed at low temperature.…”

Evolution of molecular ordering and phase transitions in C60/C70solid solutions

“…Following the methods and considerations given in Ref. [32], it is found that ∆U 1q is given by equations of identical form as Eq. (10) but with a new constant γ that depends on x as follows…”

“…We follow closely the procedures and notation given in Refs. [31,32] except that here we consider the case of dipole alignment in the 〈111〉 direction of the original cubic cell. In the rhombohedral elastically ordered phase (R3m), C 70 molecules aligned in 〈111〉 direction can lie in four different orientations q = 1 − 4.…”