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Transmission electron microscopy (TEM) is an excellent characterization method to analyze the size, morphology, crystalline state, and microstructure of perovskite quantum dots (PeQDs). Nevertheless, the electron beam of TEM as an illumination source provides high energy, which causes morphological variation (fusion and melting) and recession of the crystalline structure in low radiolysis tolerance specimens. Hence, a novel and facile strategy is proposed: electron beam peel [PbBr6]4− octahedron defects from the surface of QDs to optimize the crystal structure. TEM and high-angle annular dark-field scanning TEM (HAADF) tests indicate that the [PbBr6]4− octahedron would be peeled from the surface of QDs when QDs samples were irradiated under high-power irradiation, and then a clear image would be obtained. To avoid interference from a protective film of "carbon deposits" on the surface of the sample when using high resolution TEM, amorphous carbon film (15–20 nm) was deposited on the surface of QDs film and then characterized by TEM and HAADF. The detection consequences showed that the defection of PbBr2 on the surface of QDs will gradually disappear with the extension of radiation time, which further verifies the conjecture. [ABSTRACT FROM AUTHOR]

Nominal (Ba1−xMgx)TiO3 (x = 0.015) (BM1T) and (Ba1−xMgx)TiO3 (x = 0.03–0.20) (BMT) ceramics were prepared by the mixed-oxide route at sintering temperatures (Ts) of 1200−1400 °C and 1200 °C, respectively. The solubility limit of Mg2+ in BMT was determined by XRD to be x = 0.05, and evidence was found for occupation of the A site by Mg2+. Electron paramagnetic resonance (EPR) was employed as a key technique to investigate the effect of Ts on oxygen vacancies in BM1T. The structure of BM1T changed from pseudocubic at Ts = 1200 °C to tetragonal at 1300 °C to mixed phases of hexagonal and tetragonal at 1400 °C. When Ts ≥ 1300 °C, a g = 1.956 EPR signal was observed at T = −188 °C and assigned as ionized oxygen vacancies. Mg2+ exhibited amphoteric behavior of substituting for the double cation sites. When Ts = 1400 °C, B-site Mg2+ and oxygen vacancies mainly existed in the hexagonal phase and A-site Mg2+ was dominant in the tetragonal phase. The higher tan δ was attributed to the higher concentrations of oxygen vacancies and Ti3+ in the hexagonal phase. [ABSTRACT FROM AUTHOR]