Eur. Phys. J. B 14, 227-238 (2000)
https://doi.org/10.1007/s100510050124

Order-disorder evolution in solid solutions of the NLO material KTiOPO₄: K_0.88Rb_0.12TiOPO₄ and K _0.465Rb _0.535TiOPO₄ in the temperature range 293-973 K ^*

¹ Laboratoire de Cristallographie et Modélisation des Matériaux Minéraux et BiologiquesLCM$^3$B ESA CNRS 7036, Université Henri Poincaré, Nancy I, Faculté des sciences, BP 239, 54506 Vandœuvre-lès-Nancy Cedex, France
² Laboratoire de Physique de l'Université de BourgogneLPUB UPRESA 5027, Faculté des sciences Mirande, BP 400, 21011 Dijon Cedex, France

Received: 22 April 1999
Published online: 15 March 2000

Abstract

K_0.88Rb_0.12TiOPO₄ and K_0.465Rb_0.535TiOPO₄ solid solutions of the potassium titanyl phosphate (KTiOPO₄, space group Pna2₁) family, are described at 293, 473, 673, 873 and at 973 K. Their high resolution structures are obtained by using accurate single-crystal X-ray diffraction techniques at high resolution, (sin Å^-1. Large anharmonic motion of alkaline ions increasing with temperature allows the evolution of the rubidium and potassium ions repartition in the two alkaline sites versus temperature. To describe this motion inducing ionic conductivity phenomenon and to determine accurately the order-disorder evolution, two alkaline site refinement models are developed and discussed. A thermodynamic model, which uses a barrier-potential model, is also developed to specify the different interactions operating in the order-disorder evolution, and more generally interactions between alkaline ions and the framework.