Effects of different valence of starting oxides on the structure and properties of Co-Mn-Fe-Zn-Ni-O high-entropy ceramics

In this work, using different manganese sources, Co-Mn-Fe-Zn-Ni-O high-entropy ceramics (HECs) were synthesized via the solid-phase method. X-ray diffraction (XRD) data showed that the HECs consist of rock salt and spinel phases, and the choice of raw materials has a great influence on the phase composition and lattice distortion of HECs. Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) analyses showed that the HECs have dense microstructures, with the major elements conforming to iso-atomic ratios. Xray photoelectron spectroscopy (XPS) and Raman spectroscopy data showed that Mn3+ ions with Jahn-Teller effects distort the [MnO6] octahedra, affecting the electrical properties and aging stability of the material. The room-temperature resistivity of the HEC systems ranged from 20.81 k Omega cm to 35.43 k Omega cm, and the B25/50 resistivity values varied between 4037 K and 4048 K. The resistance drift was observed to be less than 0.70 % after aging at 125 degrees C for 1000 h. Impedance analyses suggested that the electrical properties of the high-entropy ceramics can be modulated by tailoring the grain size and grain boundary morphology. Selecting suitable raw materials based on valence-induced effects and the tendency of ions to occupy specific sites offers new insights into the design and synthesis of tailor-made high-entropy NTC ceramics.