Structure and properties of lanthanum–aluminum–phosphate glasses

Glass-forming characteristics, properties and structural features of glasses in the La2O3–Al2O3–P2O5 system have been investigated. The glass-forming region is small compared to the Na2O–Al2O3–P2O5 system. Glass transition temperature increases and thermal expansion coefficient, refractive index, and density all decrease as the alumina content of the glass is increased. Infrared (IR) spectroscopy indicates that the glass network is dominated by bridging P-tetrahedra with terminal tetrahedra present in glasses with O/P ratios >3. 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy indicates that Al ions are incorporated in these glasses in 4-, 5-, and 6-coordinated sites. The average Al-coordination number (CN) increases with an increase in the Al/La ratio and decreases with an increase in the O/P ratio. Both trends can be explained by the avoidance of Al–O–Al bonds in the glass structure.