Knudsen effusion mass spectrometric approach to the thermodynamics of Na 2O–Nb 2O 5 system

Abstract

Knudsen effusion mass spectrometry (KEMS) was used to determine the equilibrium vapour pressures of sodium over five selected compositions in different solid two-phase regions of the Na 2O–Nb 2O 5 system at 1100–1470 K. The results were then used to determine the standard thermodynamic functions ( Δ f G T ° , Δ f H 298 K ° , S T ° ) of five solid compounds: Na 3NbO 4, NaNbO 3, Na 2Nb 4O 11, NaNb 3O 8 and NaNb 13O 33. These data were then incorporated into the IVTANTHERMO database to perform equilibrium calculations under real conditions relevant to the high temperature stability of sodium niobate, which is an important end member of the alkali niobate-based lead-free piezoelectric ceramics.