High piezoelectricity in low-temperature sintering potassium–sodium niobate-based lead-free ceramics

Abstract

Here we have realized three goals in a new potassium–sodium niobate material using CuO as sintering aid, such as low temperature sintering, the suppression in the loss of alkali metals, and attaining a high d₃₃. Low-temperature sintered 0.96(K_0.46Na_0.54)Nb_0.95Sb_0.05O₃–0.04Bi_0.5(Na_0.82K_0.18)_0.5ZrO₃ ceramics were made conducting by adding CuO using an ordinary ceramic fabrication technique. The sintering temperatures drop from 1095 °C to 950 °C when the CuO content is increased from 0 to 2.5 wt%, and the K and Na loss could be also prevented under a low processing temperature. In addition, the ceramics undergo a phase transition with increasing CuO content, such as from a rhombohedral–tetragonal phase coexistence to the mixture of both rhombohedral–orthorhombic and orthorhombic–tetragonal phase boundaries. The inhomogeneous Cu²⁺ distributions become more obvious as the CuO content rises, i.e., the excess Cu²⁺ aggregates at the small grains region for a low CuO content (x ≤ 1.5), and at the small and large grains zones for x = 2.5. The dielectric constant gradually decreases as the CuO increases, and the dielectric loss is lowered by adding CuO content. A well polarization vs. electric field (P–E) loop is seen in the ceramics with x ≤ 2.5, and those with x = 2.5 possess a high d₃₃ of 310 pC N⁻¹ even if the sintering temperatures drop down to 950 °C. As a result, it is an efficient way to promote the piezoelectricity of copper oxide-modified alkaline niobate ceramics using a low-temperature sintering technique.