Crystal growth, structure, and dielectric properties of layered cobaltates La2−xSrxCoO4 (x = 0.4, 0.5, and 0.6) single crystal

• La2−xSrxCoO4 (x = 0.4, 0.5, and 0.6) crystals have been successfully grown by FZ method.
• The c-axis of as-grown crystals is perpendicular to the growth direction.
• The origination of giant dielectric constant is the mixed-valence Co2+ and Co3+.
• The dielectric relaxation shows a thermal-activated behavior.

In this work, La2−xSrxCoO4 (x = 0.4, 0.5, and 0.6) crystals with the Ruddlesden–Popper K2NiF4-type structure have been grown by the floating zone method. This compound crystallizes in the K2NiF4-type structure with space group I4/mmm. Temperature-dependent dielectric properties of the as-grown crystals were studied over a broad frequency range. The origin of the giant dielectric constant in this system is the mixed-valence structure between Co2+ and Co3+, and the dielectric constant at high frequency is related to the charge ordering structure. The dielectric relaxation shows a thermally-activated behavior. The corresponding activation energy (assigned to small polaronic hopping) can be obtained by Arrhenius fitting.

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