Evidence of Cr³⁺ and Cr⁴⁺ Coexistence in Chromium-Doped SnO₂ Nanoparticles: A Structural and Magnetic Study

Abstract

The present study reports the successful synthesis of Sn1–xCrxO2 nanoparticles with doping content (x) ranging from 0 to 0.20. Samples were synthesized by a polymer precursor method using SnCl2·H2O and Cr(NO3)3·5H2O as metal ion suppliers. In all samples X-ray diffraction data show one single-phase formation (rutile-type), with crystalline size (crystal strain) decreasing (increasing) monotonically while increasing the x content, which are assigned to substitutional solution of Cr and Sn ions in the crystalline structure. In addition to a weak magnetic ordering observed in a few samples (x = 0.01, 0.02, 0.03, and 0.05), paramagnetism is the main magnetic contribution in all synthesized samples, which is due to the presence of two chromium ions (Cr3+ and Cr4+). X-ray photoelectron spectroscopy measurements confirm the coexistence of Cr3+ and Cr4+ ions in excellent agreement with the monotonic decrease of the [Cr3+]/[Cr4+] versus doping content (x), assessed from the fitting of the susceptibility versus temperature data using the Curie–Weiss law.