Single‐step preparation of rutile‐type CrNbO₄ and CrTaO₄ oxides from oxalate precursors–characterization and properties

Abstract

Chromium niobate and tantalate (CrNbO4 and CrTaO4) were synthesized by pyrolysis of the oxalate‐based heterometallic complexes [Cr2(bpy)4(μ‐O)4Nb2(C2O4)4]·3H2O (Cr‐Nb) and [Cr(bpy)2(H2O)(μ‐O)Ta(C2O4)3]2·3.5H2O (Cr‐Ta) (bpy = 2,2'‐bipyridine). Compared to conventional solid‐state synthesis, herein studied oxides are prepared at lower temperatures, in one step without repeating grinding procedures. The structure, morphology, and optical properties of the as‐synthesized oxides were characterized using powder X‐ray diffraction (PXRD), field emission scanning electron microscopy (SEM), the thermogravimetric and differential thermal analysis (TG/DTA) and UV‐vis diffuse reflectance spectroscopy (UV‐vis DRS). The determined band gap energies of CrNbO4 and CrTaO4 are 2.39 and 2.82 eV, respectively, which prompted us to investigate photocatalytic activity of these oxides in degradation of dyes. Microscopy studies show that the particles of both oxides began to aggregate into bigger particles, leading to an increase in grain size. Additionally, magnetization measurements on both oxides revealed spin‐glass behavior at low temperatures.

A prediction of the thermodynamic, thermophysical, and mechanical properties of CrTaO4 from first principles

“…Experimental results from ref. 38 indicated that CrTaO 4 possesses a rutile‐type structure. It is well‐established that the prototype of the rutile phase is TiO 2 , which exhibits a space group of P 4 2 / mnm .…”

“…The results depicted in Figure 2b indicate that the C 2/ m structure remains the most stable phase in the entire temperature range from 0 to 2000 K followed by the I 4 1 md and P 2/ c phase, but the difference in total energy is extremely small, 0.002 eV/atom, which is well within the uncertainty range of DFT calculations especially for oxides. Various experimental results show that the stable crystal structure for CrTaO 4 is the rutile I 4 1 md 37,38 . There are several reasons that may contribute to the discrepancy in the phase stability of CrTaO 4 between DFT prediction and experiments.…”

“…Various experimental results show that the stable crystal structure for CrTaO 4 is the rutile I4 1 md. 37,38 There are several reasons that may contribute to the discrepancy in the phase stability of CrTaO 4 between DFT prediction and experiments. It is known that the accuracy of DFT calculations rely on the exchange-correlation functional used to describe the electron-electron interactions especially for the transition metal oxide system.…”

Microstructure, elastic/mechanical and thermal properties of CrTaO 4: A new thermal barrier material?

“…From Fig. 1(a), one can see that the hallmark in the TG curve is a mass loss of about 0.358%, which can be attributed to the evaporation of Cr 2 O 3 at high temperatures [24]. In the DSC curve, there is a wide exothermic peak in the temperature range of 1030−1110 ℃.…”

A 3D oxalate‐bridged [CuIIFeII] coordination polymer as molecular precursor for CuFe2O4 spinel—photocatalytic features

“…This paper outlines the use of the CP [Cu II Fe II 2 (H 2 O)(terpy)(C 2 O 4 ) 3 ] n ( 1 ; terpy = 2,2′:6′,2″‐terpyridine) 25 as an efficient photocatalyst for the photodegradation of rhodamine B (RhB, C 28 H 31 ClN 2 O 3 ) and methylene blue (MB, C 16 H 18 N 3 SC) dye pollutants, as well as a single molecular precursor for the preparation of the CuFe 2 O 4 spinel due to the suitable metal ratio by thermal treatment 26–30 . Namely, the oxalate group, C 2 O 4 2− , easily decomposes at low temperatures into gaseous CO 2 and CO, and therefore, the oxalate‐based solids can serve as suitable precursors for the preparation of mixed metal oxides 11,26,28,31–33 . In this work, we are the first ones to deliver a brief scheme on developing the feasible molecular precursor‐to‐material route for the preparation of CuFe 2 O 4 spinel as viable alternative to various hydrothermal/solvothermal pathways.…”