Estudo estrutural da fase modulada dos compostos mistos K2MOxW(1-x)O4 por difração de Raio X

Abstract

The potassium molybdate (K2MoO4) and potassium tungstate (K2WO4) have been studied since middle sixties. Despite the great number of published works on the crystallographic structure of such compounds, some facts are still unexplained. These compoundsbelong to the A0A00BX4 family, which has been widely studied due to the huge amount of different crystallographic phases they exhibit; in many cases a modulated phase is observed. In the present work, results related to the different phases of potassium molybdate potassium tungstate and the mixed compound K2Mo0.5W0.5O4 are presented. Themain point of this dissertation is the study of the intermediate modulated phase of the K2MoxW(1-x)O4. A new interpretation for this phase is proposed based on a structural model which describe the crystal as being composed by three orthorhombic domains, rotated by 1200 with respect to each other. X-ray powder diffraction was used in most ofthe experiments, and the Rietveld method for structural refinement was widely used on the analysis process.