Aqueous Sol–Gel Route toward Selected Quaternary Metal Oxides with Single and Double Perovskite-Type Structure Containing Tellurium

Highly crystalline SrFe 2/3 Te 1/3 O 3, Ba 3 Fe 2 TeO 9, and Ba 2 NiTeO 6 have been synthesized by using a specially developed sol–gel route methodology, reducing the time needed employing solid-state routes and resulting in high reaction yield up to 75%. These materials have been studied by X-ray powder diffraction (XRPD), scanning and transmission electron microscopy, Raman spectroscopy, and dielectric and magnetic measurements. At room temperature, the crystal structure of SrFe 2/3 Te 1/3 O 3 is cubic, space group Pm 3̅ m, with a = 3.9373(2) Å, whereas Ba 3 Fe 2 TeO 9 crystallizes in the hexagonal crystal system, space group P 6 3 / mmc, a = 5.7691(4) Å, and c = 14.208(1) Å. The third studied perovskite Ba 2 NiTeO 6 crystallizes in the trigonal R 3̅ m space group with a = 5.7974(4) Å and c = 28.599(2) Å. Based on structural characterization results, the obtained single and double perovskite crystallites are nearly in nanometer regime, ranging from 45 to 164 nm, building micrometer-sized particles with visible well-faceted hexagonal morphology. Magnetic measurements show the onset of ferrimagnetic ordering at relatively high temperature of 667 K for the SrFe 2/3 Te 1/3 O 3, whereas Ba 3 Fe 2 TeO 9 and Ba 2 NiTeO 6 show antiferromagnetic ordering below 80 and 8.6 K, respectively. The measured room temperature dielectric constants are in the range between 15 and 77.