Effects of vanadium doping on sintering conditions and functional properties of NbLi co-doped PZT ceramics. Comments on Li location

•Effects of 1 and 2 mol % vanadium in NbLi co-doped PZT ceramics were studied.•V decreases the sintering temperature and promotes a harder piezoelectric behaviour.•V increases the lattice tetragonality and grain size.•Partial reduction of V5+ to V4+ ions and the occurrence of defects are observed.•Li location was indirectly deduced from the experimental results.

The effect of 1 and 2 mol % V addition on sintering conditions, structural and functional properties of NbLi co-doped PZT ceramics, prepared by conventional ceramic method, was systematically studied, by different experimental techniques. The reported results show that the increasing amount of vanadium, as a substitute for niobium, decreases the optimal sintering temperature with 100–150 °C, but slightly reduces the piezoelectric, ferroelectric, and electromechanical properties of these ceramics. In addition, the presence of vanadium increases the lattice tetragonality and grain size, promoting a harder piezoelectric behaviour, mostly in the absence of niobium. EPR spectra exhibit well-defined hyperfine splitting characteristics for V4+ state, dispersed in the lattice as VO2+ ion. Additionally, complex paramagnetic defects (charged oxygen vacancies and associated defects) are evidenced for 2 mol % vanadium addition. The results were explained by assuming that vanadium promotes the B-site Li substitution, compensated by oxygen vacancies, while niobium facilitates the A-site Li substitution with lead vacancies formation and partial reduction of V5+ to V4+. Thus, indirect information about lithium location is provided.