High-resolution neutron powder diffraction data were collected at different temperatures and pressure under hydrogen or oxygen under high and low humidities. The samples were loaded in sealed quartz tubes in dry or wet conditions at 0.33 atm pressure and 295 K temperature, and heated up to 973 K during measurements. Rietveld refinement of neutron diffraction data showed that the structure changed from primitive orthorhombic (space group Pbnm) to body centred orthorhombic (Imma) to rhombohedral (R-3c) on heating from room temperature to 973 K. At 623 K temperature and 0.71 atm pressure, the unit-cell volume is higher in wet hydrogen and oxygen atmosphere than dry atmosphere due to proton uptake. Oxygen site occupancies were directly determined as functions of temperature for dry and wet conditions in both oxidising and reducing conditions in order to probe actual oxygen/hydroxyl contents under the conditions relevant to most fuel cell or transport studies. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.