UC San Diego

The perovskite structure is very common in ceramics. In this thesis, eleven kinds of high-entropy ABO3 perovskites, with five equimolar atoms in B sites, were successfully synthesized by high-energy ball milling and conventional pressureless sintering. Six of them, compositions #S1, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Mn0.2)O3, #S5, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, #B2, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Ce0.2)O3, #B3, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Y0.2)O3-x, #B5, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, and #BS1, (Ba0.5Sr0.5)(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, can form a cubic homogeneous single phase, while the others showed a major cubic phase with different amount of secondary phases. Phase purity was verified by energy dispersive x-ray spectroscopy (EDS) mapping. Quench experiments were carried out to prove that composition #S1, Sr(Zr0.2Sn0.2Ti0.2Hf0.2Mn0.2)O3, is an entropy stabilized perovskite, which is also characterized in atomic and nanoscale by aberration-corrected scanning transmission electron microscopy (AC STEM), STEM high-angle annular dark-field (HAADF) images, and STEM annular bright-field (ABF) images. Goldschmidt's tolerance factor (t) was introduced to be a necessary, but not sufficient, condition to form a homogeneous single phase, while the revised Hume-Ruthery rule for high-entropy alloys (HEAs) can not extend to the case of high-entropy ABO3 perovskites. The successful synthesis of these high-entropy ABO3 perovskites reveals the possibility to create high-entropy cubic ceramics and to discover new materials in ABO3 perovskites family.