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A 3D heterometallic oxalate‐bridged coordination polymer [CuIIFeII2(H2O)(terpy)(C2O4)3]n (terpy = 2,2′:6′,2″‐terpyridine) (1) was investigated both as photocatalyst for the organic dye removal and as a single‐source precursor for the preparation of the copper ferrite (CuFe2O4) nanocrystals by thermal processing. The dual functionality of 1 was supported by the degradation of aqueous solutions of rhodamine B (RhB) and methylene blue (MB) solutions under visible (Vis) and ultraviolet (UV) light irradiation, powder X‐ray diffraction data collection at room temperature, and the optical and scanning electron microscopy analyses. A close inspection of the X‐ray diffraction patterns unveiled qualitative and quantitative information on the phase composition obtained after the single‐source molecular precursor route to spinel oxide. By optimizing the temperature levels and setting the controlled heating rate at 6 h of holding time, the phase composition of thermal processing of 1 was evaluated—thermal treatment of 1 at 950°C for 6 h and a heating/cooling rate of 10°C min−1 resulted in the formation of solely tetragonal spinel phase of CuFe2O4, whereas the formation of both tetragonal and cubic CuFe2O4 phases was observed at 950°C by the heating rate of 30°C min−1. To obtain the high‐temperature cubic CuFe2O4 oxide, compound 1 was heated and then quenched at 925°C, which led to the formation of the cubic spinel ferrite as the main crystalline oxide phase. Moreover, the photocatalytic properties of the t‐CuFe2O4 spinel were investigated under the same conditions as for 1. The optical bandgap energies were estimated from UV–Vis absorption spectra for both metal oxide and precursor powder. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ferroelectrics play an important role in various applications, from electronics to mechanics, optics, and biomedicine. Here, the preparation of a series of block copolymer–templated mesostructured (lead‐free) oxide ferroelectrics is described. Distorted perovskite LiNbO3, LiTaO3, and solid solution LiNbO3–LiTaO3 are produced as single‐phase thin films of good quality by the dip‐coating method using an evaporation‐induced self‐assembly process. They are investigated by a combination of electron microscopy, X‐ray diffraction and scattering, X‐ray photoelectron spectroscopy, and time‐of‐flight secondary ion mass spectrometry. Thermal treatment at ≥600 °C is required to initiate crystallization. Both the pore ordering and thermal stability increase with increasing tantalum content. Ferroelectric testing through dynamic and remanent polarization experiments at ambient conditions confirm the uniformity and purity of the LiNbO3 thin‐film system. Results from positive‐up and negative‐down test measurements reveal a stable switching polarization of 2 µC cm−2, with a coercive field of 50 kV cm−1. Taken together, the lithium niobium and tantalum oxides prepared in the work are rare examples of sol–gel derived perovskite‐type materials with an ordered mesoporous morphology. Because of the spontaneous electrical polarization observed for LiNbO3, such block copolymer–templated thin films might pave the way for the development of a new class of 3D nanocomposite ferroics. Ferroelectric LiNbO3, LiTaO3, and solid solution LiNbO3–LiTaO3 are successfully produced as continuous cubic mesoporous thin films of high crystallinity by the dip‐coating method using a facile coassembly strategy. Remanent polarization measurements conducted at ambient conditions on the sol–gel derived LiNbO3 material demonstrate a stable and robust (macroscopic) switching polarization. [ABSTRACT FROM AUTHOR]