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

• 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.

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.