High-density sol-gel derived, cold-isostatically pressed La0.67Ca0.27Sr0.06MnO3 polycrystalline ceramics and their room-temperature TCR improvement

Abstract

In this study, high-density La0.67Ca0.27Sr0.06MnO3 (LCSMO) ceramics were successfully obtained by sol-gel method followed by cold isostatic pressing (CIP) under 250 MPa. Effects of sintering temperature (TS, 1250 °C ≤ TS ≤ 1450 °C) on structure, surface chemical, electrical, and optical properties of as-obtained LCSMO ceramics were investigated by X-ray diffraction (XRD, BDX3200), X-ray photoemission spectroscopy (XPS, Thermo Fisher Scientific), a four-probe system (East changing ET9005), Fourier transform infrared spectrometry (FTIR, TENSOR 27), Raman microscopy (RENISHAW inVia) and UV–vis spectrophotometry (HITACHI U-4100), respectively. All prepared samples showed orthorhombic structure with Pnma space group. As TS increased, grain size gradually rose from 2.71 to 7.30 μm. XRD refinement, Raman, and FTIR all depicted constant of bond angle and length of Mn–O. Hence, variation in TS did not cause lattice distortion inside samples. The best electrical properties were obtained at 1450 °C, where resistivity (ρ) fell below 0.008 Ω cm and temperature coefficient of resistivity (TCR) reached 13.0% K−1 at 289.2 K (room temperature).It is worth noting that electrical performance was indeed improved due to high densities of samples under processing of CIP. Overall, the change in TS from 1250 to 1450 °C greatly influenced electrical behaviors but showed little effect on structural and optical properties of LCSMO ceramics.