The effects of doping 60 P2O5-40 Fe2O3 (mol%) glasses with 5-10 mol% SiO2, Al2O3 or B2O3 on their thermal stability, iron environments and redox were investigated. Thermal stability improved markedly with 5% dopant addition in the order Al2O3 > SiO2 > B2O3 > base glass. Solubility of pro rata additions when melted at 1150 degrees C was 5-10% SiO2, < 5% Al2O3, and > 10% B2O3. It was possible to dissolve 5% Al2O3 by replacing Fe2O3. These additions generally had little effect on dilatometric measurements and iron environments, however the Fe2+/Sigma Fe redox ratio increased in the order base glass < Al2O3 < SiO2 < B2O3. This behaviour was broadly consistent with the effects of glass basicity. The increased thermal stability of these glasses may improve their suitability for applications such as waste immobilisation or sealing. (c) 2006 Elsevier Ltd. All rights reserved.