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The influence of methanol and ­NH4Cl on solvothermal ZnO synthesis and properties Oscar Marin1,2   · Vanessa González1,2 · Nicolás Budini3 · Mónica Tirado2,4 · David Comedi1,2 Received: 4 March 2020 / Accepted: 14 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract Powders composed of ZnO sub-microspheres were obtained in two stages: solvothermal synthesis and thermal annealing at 125, 300, 450 or 600ºC in atmospheric conditions. The synthesis was carried out with methanol as solvent, zinc acetate dihydrate as ­Zn2+ source and ammonia chloride as complexing agent. The as-grown and annealed samples were studied through photoluminescence, microRaman and reflectance spectroscopies, scanning electron microscopy and X-ray diffraction (XRD). After the solvothermal synthesis stage, a white precipitate was obtained composed of a flower-like multiphase assembly of layers identified mainly as a layered basic zinc salts (LBZS) and Zn(NH3)2Cl2. After the annealing treatments, the LBZS and Zn(NH3)2Cl2 transformed into ZnO, while the powder morphology changed from the layered flower-like to polycrystalline ZnO spherical particles with sub-micrometer diameters. With increasing annealing temperature, the ZnO spheres size remained unchanged, while the mean crystallite size and wurtzite lattice parameters decreased as a result of tensile stress relaxation. Concomitantly, a blueshift of the defect-related ZnO emission was observed. The combined analysis of emission, vibrational and reflectance spectra and XRD suggests that the annealing treatments result in the formation of ZnO crystallites with oxygen vacancies and oxygen vacancy-zinc interstitial complexes whose densities increase as the annealing temperature increases. The results and analysis reported in this work contribute to the understanding of growth mechanisms relevant for the tailoring of ZnO powder properties through solvothermal synthesis in non-aqueous media. Keywords  ZnO microspheres · Solvothermal technique · Non-aqueous synthesis · Photoluminescence · MicroRaman · Williamson–Hall method Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s0033​9-020-03636​-w) contains supplementary material, which is available to authorized users. * Oscar Marin [email protected] * David Comedi [email protected] 1



NanoProject y Laboratorio de Física del Sólido (LAFISO), Departamento de Física—Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán, Avenida Independencia 1800, San Miguel de Tucumán, Argentina

2



Instituto de Física del Noroeste Argentino–INFINOA (CONICET–UNT), Tucumán, Argentina

3

Instituto de Física del Litoral‑IFIS (CONICET–UNL) y Departamento de Física, Facultad de Ingeniería Química, Universidad Nacional del Litoral, Santa Fe, Argentina

4

NanoProject y Laboratorio de Nanomateriales y Propiedades Dieléctricas (LNPD), Departamento de Física, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán, Avenida Independencia 1800, San