Physical Chemistry of the PbO-MgO-Nb2O5-TiO2 System for Ferroelectric Relaxors

• Main Author: Petuskey, William T.
• Other Authors: ARIZONA STATE UNIV TEMPE DEPT OF CHEMISTRY
• Format: Text
• Language: English
• Published: 2004
• Subjects: Physical Chemistry; Electricity and Magnetism; *FERROELECTRIC MATERIALS; *PHYSICAL CHEMISTRY; *LEAD OXIDES; CRYSTAL STRUCTURE; THERMODYNAMICS; THERMOCHEMISTRY; GRAVIMETRY; TERNARY COMPOUNDS; QUATERNARY COMPOUNDS; TITANATES; SOLID SOLUTIONS; CHEMICAL EQUILIBRIUM; PHASE DIAGRAMS; VAPORIZATION; SOLID PHASES; PEROVSKITES; MAGNESIUM OXIDES; NIOBATES; KNUDSEN GAGES; LEAD MAGNESIUM NIOBIUM TITANATE SYSTEM; *RELAXORS; Knudsen; Orca
• Online Access: http://www.dtic.mil/docs/citations/ADA420896; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA420896

This project was devoted to evaluating the phase chemistry and thermochemistry of the quaternary lead-magnesium-niobium titanate system (PbO-MgO-Nb2O5-TiO2). It is technologically relevant to the development of ferroelectric relaxors with the perovskite crystal structure and of the general composition Pb(Mg(0.33-0.33)xNb(0.67-0.67x)Ti(x))O. This project also evaluated the phase chemistry of most of the remaining compositions of the system. The four ternary phase diagrams of PbO-MgO-Nb2O5, PbO-MgO-TiO2, PbO-Nb2O5-TiO2 and MgO-Nb2O5-TiO2 at 1000 degrees C were determined in some detail. The quaternary phase diagram was evaluated for relatively PbO-poor compositions. In addition, the thermochemistry of the overall system was also evaluated between about 800 and 1000 degrees C, characterized in the form of equilibrium vaporization rates of lead oxides. This was accomplished by Knudsen cell gravimetry on binary, ternary and quaternary phase states that were thermodynamically well defined. From this, the formation thermodynamics of a number of solid phase compositions were determined for the first time. Moreover, trends were evaluated of the equilibrium vapor pressures over perovskite solid solutions as a function of composition. ORCA proposal: 01-1198.