Effect of isovalent substitution on microstructure and phase transition of LaNb1−xMxO4 (M=Sb, V or Ta; x=0.05–0.3)

• Antimony doped lanthanum niobate was successfully synthesized by solid state synthesis method.
• The structural properties have been investigated by XRD and SEM.
• The influence of doping on phase transition temperature has been studied.

LaNb1−xMxO4 oxides with pentavalent elements of different ionic sizes (M=Sb, Ta and V, x=0.05–0.3) were synthesized by the solid state reaction method. Special interest was devoted to the antimony substituted lanthanum niobate which is a new material in this group. Rietveld analysis of the X-ray diffraction patterns was used to determine the influence of the material composition on unit cell parameters. On the basis of dilatometric measurements phase transition temperatures and thermal expansion coefficients of the studied materials were determined. It was shown that with increasing concentration of Sb the phase transition temperature decreases. Thermal expansion coefficient of the antimony substituted samples above the transition temperature is in the range from 8.1 to 9.1×10−6 1/K, whereas below the transition temperature the TEC value is between 14 and 17.3×10−6 1/K. Influence of Ta, V and Sb substitutions on the microstructure and grain size was studied.

Substitution of niobium by other pentavalent elements in LaNbO4 leads to change in phase transition temperature. In case of Sb substituent a shift of phase transition into the lower temperature region is observed. LaNb0.7Sb0.3O4 substitution allows to achieve material with tetragonal crystal structure at room temperature and no phase transition up to 1000 °C.Figure optionsDownload as PowerPoint slide