Interlayer alkali ion governs robustness, reactivity, and dielectric properties of sintered lepidocrocite titanate

Abstract

We investigate the structure across different length scales including the dielectric properties of Cs0.7Zn0.35Ti1.65O4, Rb0.75Zn0.375Ti1.625O4, and K0.8Zn0.4Ti1.6O4 sintered at TS ​= ​900–1100 ​°C, where the lepidocrocite-type crystal structure is preserved. The increasing interlayer distance in the Rb-/K-analog is explained by the alkali loss which reduces the electrostatic attraction between the sheets and the interlayer ion. Meanwhile, the interlayer contraction in the Cs-analog is rather unusual. The increasing (decreasing) interlayer distances correlate to upshift (downshift) of the Ti-O vibration in the Raman spectra. The three compositions show varied grain orientation depending on the interlayer ion and TS. The dielectric permittivity differs by one order of magnitude in the order Cs0.7Zn0.35Ti1.65O4 « Rb0.75Zn0.375Ti1.625O4 « K0.8Zn0.4Ti1.6O4, suggesting the interlayer ion as the dominating dipole. The influences of TS, pellet density (i.e., alkali loss), and grain size/morphology/orientation on the dielectric permittivity are discussed. The understanding of the response to a high temperature treatment would be beneficial not only to specimen fabrications for physical properties measurements, but also to applications where the thermal stability is of concern.