Effect of pH variation on citrate nitrate sol-gels obtained from auto-combustion method: Synthesis, calculations and characterisations of extremely dense BaZrO3 ceramic

We report the formation of phase pure, uniform, nano-sized and extremely dense BaZrO3 ceramic employing the sol-gel auto-combustion synthesis technique by fixing the metal to citrate ratio as 1.5 and systematically varying the pH of the gel. The details of the species that were formed during the gel stage were investigated by calculating the pH variation of the relative concentration of the barium and zirconium citrate species whose presence was indicated in solid-state NMR spectra that displayed extra resonance lines. Sintered density of the pellet obtained at a sintering temperature of 1550°C was found to be the highest for pH = 1 pellet, indicating that the gel structure for this pH was the most homogeneous which resulted in the formation of numerous sites of the resultant BaZrO3 ceramic that are evenly dispersed without agglomeration. The obtained percentage density was 99.9%, the highest ever-reported density of BaZrO3 ceramic by any technique.