Effect of Li⁺ ion occupancy on microstructure and dielectric characteristics in KSr₂Nb₅O₁₅ tungsten bronze ceramics

Highlights: • Li-doped KSr2Nb5O15 (KSN) ceramics were prepared by using fine KSN crystalline as raw material. • A small addition of Li2CO3 was effective in inhibiting the abnormal grain growth and crack formation. • Dielectric spectra of Li-doped KSN ceramics displayed temperature-stable dielectric constant and two dielectric anomalies. - Abstract: Li-doped KSr₂Nb₅O₁₅ (KSN) tungsten bronze ceramics were prepared by the conventional solid-state method. Fine KSN crystalline fabricated by a two-step molten salt synthesis were used as raw material. The effects of Li₂CO₃ content on microstructure and dielectric properties of the ceramics were investigated. It was found that a small addition of Li₂CO₃ was effective in inhibiting the abnormal grain growth and crack formation. Investigations of the microstructure indicated that grain size transformed from normal to bimodal distribution when Li₂CO₃ content was increased. For the case of 8 mol%, a unique keyboard structure was observed in coarse grains. Dielectric spectra of all compositions displayed temperature-stable high dielectric constant. A broad low temperature relaxor-like dielectric anomaly was observed in addition to the high temperature maximum around 70°C. It was interesting to note that the high temperature peak gradually became significant with the increase of Li₂CO₃ content.