Sintering and properties of lead-free (K,Na,Li)(Nb,Ta,Sb)O3 ceramics

Two different stoichiometric (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 and non-stoichiometric (K0.38Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04) O2.97 compositions were prepared by the conventional mixed oxide and carbonate route. Low temperature synthesis process at 700 °C for 2 h, and further attrition milling process resulted in agglomerated powder of 500 nm of primary particles in the range of 50–70 nm. The ceramics sintered at 1125 °C showed the highest densification that decreased for higher sintering temperatures. Non-stoichiometric composition densification process was assisted through the presence of a liquid phase that promotes grain growth and the appearance of a secondary ferroelectric phase with tungsten–bronze type structure. The samples showed a relaxor type behaviour that diminished because of the compositional homogeneity improvement of the liquid phase in the non-stoichiometric samples. The higher piezoelectric properties were obtained for the samples with high ferroelectric type dielectric constant versus temperature behaviour. In the non-stoichiometric samples piezoelectric constant d33 values reach ∼200 pC/N.