Raman Scattering in Medium and High Entropy Rocksalt Oxides

The Temperature Dependence (4-300K) of the Raman Scattering spectrum of various polycrystalline single phase rocksalt high or medium entropy oxides has been measured. The samples were prepared by mixing equimolar amounts of either four or five of the binary oxides (MgO,CoO,NiO,CuO,ZnO) and sintering at or above 1000^oC followed by air-quenching. The samples can be classified as either high entropy oxides (5-HEO) for mixtures of all five binary oxides, or medium entropy oxides (4-MEO) for mixtures of equimolar amounts of four binary oxides depending on the value of mixing entropy. Xray diffraction (XRD) indicated that the majority of samples were single fcc phase except for the 4-MEO (-Ni). The samples all showed similar Raman scattering spectra containing three main peaks near 545, 1096 and 1650 cm^-1 with satellite shoulders on the low frequency tail of the main peaks. The Raman spectra will be interpreted in light of the antiferromagnetic transitions exhibited by all the samples.