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Phosphate glass; thermal expansion coefficient; microhardness; optical gap.

Sodium aluminophosphate glasses having compositions of 𝑥Al₂O₃(1 – 𝑥)NaPO₃ (𝑥 = 0.05–0.2) were prepared using conventional melt-quench technique. Density, glass transition temperature, microhardness (MH), thermal expansion coefficient (TEC) and transmission characteristics were measured as a function of alumina content for different samples. They were found to depend on O/P ratio with pronounced changes taking place for O/P ratio ≥ 3.5. Density, glass transition temperature and microhardness were found to increase up to 15 mol% of alumina and then they showed a decreasing trend. Thermal expansion coefficient decreased continuously with alumina content. Optical gaps for different glass samples as measured from transmission characteristics were found to be in the range 3.13–3.51 eV. It initially decreased with alumina content up to 15 mol% and then increased. The behaviour was explained on the basis of change in the average aluminum coordination number from six Al(6) to four Al(4) (i.e. Al(OP)₆/Al(OP)₄ ratio) along with the changes in polyhedra linkages in the glass network due to change in O/P ratio.

K V Shah¹ V Sudarsan² M Goswami¹ A Sarkar¹ S Manikandan¹ Rakesh Kumar¹ B I Sharma¹ V K Shrikhande¹ G P Kothiyal¹

1. Technical Physics and Prototype Engineering Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
2. Novel Materials and Structural Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

Published

December 2003

Manuscript received

10 July 2003

Manuscript revised

20 September 2003