Effect of Zr4+ on the microstructure and electrical properties of 0.6Y2O3-0.4YCr0.5Mn0.5O3 NTC ceramics

In this study, 0.6Y 2 O 3 -0.4YCr 0.5 Mn 0.5 O 3 negative temperature coefficient (NTC) ceramics doped with different ZrO 2 contents were prepared using a two-step sintering method. The effects of Zr 4+ content on the microstructure and electrical properties of 0.6Y 2 O 3 -0.4YCr 0.5 Mn 0.5 O 3 were mainly investigated. For the microstructure, X-ray diffraction (XRD) reveals the presence of two main crystalline phases in the samples: Y 2 O 3 and YCr 0.5 Mn 0.5 O 3 . Scanning electron microscopy (SEM) reveals a clear two-phase appearance, and the porosity tends to decrease with the addition of ZrO 2 . Combined with energy dispersive spectrometer (EDS) to derive the distribution of the elements, Zr 4+ is mainly present in the Y 2 O 3 phase, with a small amount in the YCr 0.5 Mn 0.5 O 3 phase. In addition, the grain sizes of different groups were counted, and the grain size of Y 2 O 3 decreased from 2.73 ± 1.80 μm to 1.65 ± 0.93 μm with the increase of ZrO 2 content. For the electrical properties, the resistance-temperature curves were measured from 298.15 K to 1073.15 K, and all the samples exhibited NTC characteristics. And with the increase of ZrO 2 content, the resistivity increased from 1.91 × 10 7  Ω cm to 1.96 × 10 8  Ω cm, and the B 25/100 value decreased from 3315 K to 1310 K. In addition, the chemical state forms of the elements on the surface of the samples were analysed by X-ray photoelectron spectroscopy (XPS), and the valence states as well as the occupancy of the transition elements Cr and Mn were analysed in detail according to the principle of multiple splitting. Finally, the mechanism of influence on microstructure and electrical properties is explained by combining the theory of grain boundary migration and thermal ceramic conductivity.