Abstract
Amorphous aluminophosphate oxynitrides (AlPON) solids with a variable nitrogen content (2.8, 3.6, 7.2, 11, 17.5 and 20%w/w) have been prepared by nitridation of AlPO 4 using gaseous NH 3. Their thermal stability below 500°C is investigated using diffuse reflectance infrared spectroscopy and mass spectrometry. Water and ammonia, coming from AlPON surface hydrolysis upon exposure to air, are desorbed around 150°C from sites involving Al–OH. At a higher temperature (350°C) terminal –PNH 2 groups are attacked by gaseous water to produce NH 3 and additional P–OH in tetrahedral co-ordination. There is a simultaneous surface reaction between –PNH 2 groups and –PO generating P–OH (tet) but no NH 3. Besides, highly nitrided AlPON samples suffers –PNH 2 condensation around 250°C to yield gaseous NH 3 in a process thermodynamically favoured but controlled by the coverage of –PNH 2 groups.
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