Substitutional Ta-doping in Y2O3 semiconductor by sol-gel synthesis: experimental and theoretical studies

The Pechini sol-gel method has been employed for the synthesis of pure and (Hf-181 ->)Ta-181-doped Y2O3 nanopowders. We performed a structural characterization from the micro to the subnanoscopic scale by means of scanning electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffraction, and time-differential perturbed gamma-gamma angular correlation (PAC) spectroscopy. The results show the formation of the cubic bixbyite structure after a thermal treatment at 1473 K. For the synthesized Ta-181-doped Y2O3, the PAC experiments demonstrate that the impurities are mainly located at both substitutional cationic sites of the bixbyite structure. The experimental investigation was complemented by performing first-principles electronic structure calculations for Ta atoms localized at the two cationic sites of the Y2O3 semiconductor structure, which allow the study of the structural and electronic modifications induced in the host system when the impurities are introduced. These calculations confirm that the measured electric-field gradients for the synthesized Ta-181-doped Y2O3 correspond to double-ionized impurities located at substitutional defect-free cationic sites of the bixbyite host structure and indicate the site occupancy preference for Hf-181(-> 181Ta) doping. The behaviour of the site preference of Ta-181 impurities with temperature is also discussed. In addition to an extensive structural and electronic characterization of pure and Ta-doped Y2O3 semiconductor, our results demonstrate that the Pechini sol-gel process is an affordable and effective way to successfully synthesize these PAC substitutional doped samples.