Synthesis and characterization of powders in the La-Al-Si-O system

Langasite (<TEX>$La_{3}Ga_{5}SiO_{14}$</TEX>) was found to have wide application as a promising piezoelectric material. It has high thermal stability of the frequency and large electromechanical coupling factor. For the further development of new compounds with langasite type structure, powders in the La-Al-Si-O system were synthesized by a modified Pechini process. The evolution of the crystalline phase during calcination was studied using TG-DTA, XRD and TEM for the precursor powders. Decomposition proceeded via dehydration and removal of excess solvents at low temperatures (<TEX>$T<500^{circ}C$</TEX>), followed by the crystallization of lanthanum aluminum silicate (<TEX>$T>800^{circ}C$</TEX>) and phase transformation to <TEX>$LaAlO_{3}$</TEX> phase (<TEX>$T>1200^{circ}C$</TEX>). Transmission electron microscopy (TEM) of the calcined powders showed diffuse hollow rings corresponding to an amorphous phase at <TEX>$800^{circ}C$</TEX> and clear diffraction patterns corresponding to a crystalline phase from the P321 space group (<TEX>$T<1200^{circ}C$</TEX>) and the R3m (<TEX>$T<1200^{circ}C$</TEX>).