Lanthanum-doped mesostructured strontium titanates synthesized via sol–gel combustion route using citric acid as complexing agent

Abstract

In the present work, a series of lanthanum-doped mesostructured strontium titanate (LMST) materials with different La/Sr ratios were synthesized via a sol–gel combustion method in the presence of citric acid as a complexing agent and Pluronic P123 as a templating agent. The effects of the amount of doped La and calcination temperature on the physicochemical properties of the LMSTs were examined using various techniques. Powder X-ray diffraction confirmed the substitution of La3+ into the SrTiO3 lattice, generating cubic perovskite LaxSr1−xTiO3, for the LMST materials calcined at 600 °C. The purity and crystallinity of the desired perovskite phase were enhanced by citric acid addition. The solubility limit of La3+ substitution at an La/Sr ratio of 0.43 was determined by structural and morphological studies. Increasing the La doping amount decreased the crystallinity and compositional homogeneity, because an La-rich amorphous phase segregated on the surface, but improved the mesoporosity. N2 physisorption measurements indicated that the LMSTs had a bimodal pore size distribution, of which the larger one was characterized by the crystallite size of mixed oxides, and the specific surface area of 24.9–37.3 m2 g−1. The formation of mesopores in the LMST materials synthesized via sol–gel combustion was explained based on a combination of soft- and hard-templating chemistries.