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Sr3Fe2WO9 and Ba3Fe2WO9 triple perovskites have been prepared in nanocrystalline form using a modified sol–gel route with citric acid as a chelating agent. These materials have been studied by X-ray powder diffraction (PXRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. At room temperature, the crystal structure of 6H-perovskite Ba3Fe2WO9 is hexagonal, space group P63/mmc, with a = 5.7577(2) and c = 14.1095(5) Å, whereas Sr3Fe2WO9 presents a tetragonal lattice, space group I4/m, with a = 5.5803(1) and c = 7.8745(3) Å. Both compounds are nanocrystalline with average crystallite sizes of 25.6(1) nm for Ba3Fe2WO9 and 35.9(1) nm for Sr3Fe2WO9 with moderate microstrain. They exhibit a disordered perovskite structure, in which Fe3+ and W6+ cations distribute randomly at the B-sites of the perovskite lattice: Sr2[Fe0.72W0.28]2a[Fe0.61W0.39]2bO6 and Ba6[Fe1.71W0.29]2a[Fe2.29W1.71]4fO18. The detected hysteresis loops with non-zero remanent magnetization and a rather large coercive field reveal ferrimagnetic ordering with ordering temperatures of 373 K for Sr3Fe2WO9 and 330 K for Ba3Fe2WO9. Magnetic measurements show the onset of ferrimagnetic ordering at relatively high temperatures of 717 and 711 K for the Sr and Ba compounds, respectively ; however the magnetization isotherms at 2 K exhibit, for H = 50 kOe, maximum magnetization values close to 0.8 μB (f.u.)−1 and 0.35 μB (f.u.)−1 for Sr and Ba compounds, respectively, although full saturation is not reached.

Structural characterization of novel Fe(III) basic acetate with 1,3,5,7-tetraazaadamantane (hexamine – HEX), [Fe3(μ3-O)(OAc)6(H2O)3)](NO3)(HEX)2(H2O)5] (1), revealed a molecular structure typical for Fe(III) basic carboxylates, with a triangular array formed by three iron atoms being equilateral and with an uncoordinated hexamine molecule and nitrate anion present in the crystal structure. Despite the hexamine molecule being uncoordinated, it plays a crucial role in the formation of a supramolecular network. The magnetic properties of the compound were characterized by magnetic susceptibility, Mossbauer and EPR spectroscopy. These studies indicate the presence of high-spin iron ions in +3 oxidation state with non-Curie-like behaviour. A small room temperature value of the effective magnetic moment and a decrease of the product χT with decreasing temperature both speak in favour of antiferromagnetic interactions between the three individual Fe(III) ions of complex 1 with a total ground state spin of St = 1/2 per trinuclear cluster. EPR spectroscopy confirmed the formation of a St = 1/2 ground state, but also suggested the presence of weak intermolecular exchange interactions between two (or more) clusters of neighbouring molecules. The temperature-dependent Mossbauer spectra show a slowing-down of the fast spin-lattice relaxation rates of the paramagnetic Fe(III) ion below about 60 K, however, yet no static spin regime is reached down to 3.6 K.

Polar perovskite materials have attracted extensive attention due to the coexistence of magnetic ground state and semiconductor band gap within the same material. For the first time triple perovskite Sr3Co2WO9 has been synthesized in the nanocrystalline form with an average crystallite size of 23 nm using a modified aqueous citrate sol-gel method. The crystal structure of Sr3Co2WO9 is cubic at the room temperature, space group Fm-3m with with lattice parameter a= 7.9073(6) Å. The formation of Sr3Co2WO9 was studied by cyclic voltammetry, UV/Vis spectroscopy and in situ X-ray diffraction method subsequently analysed by the Rietveld analysis. The detected hysteresis loops reveal ferrimagnetic ordering with Curie temperature of 144 K. The measured effective magnetic moment of 3 mB is close to the expected value for rarely observed intermediate spin S = 1 but can also be explained as a combination of HS (40 %) Co3+ and LS (60 %). The compound exhibits the semiconducting properties with the optical band gaps equal to 3.52 eV (indirect) and 3.76 eV (direct), respectively, calculated from UV/Vis absorption spectrum using the Tauc method. Semiconducting nature was also confirmed by AC conductivity measurements, which is between 10−5 and 10−4 Ω−1 cm−1. The frequency dependent dielectric constant was explained by employing the Maxwell-Wagner model. The frequency dependent AC conductivity follows the universal Jonscher’s power law. This material could be a good candidate for implementation as a constituent for devices where its semiconducting properties would be spin controlled.

A modified aqueous sol-gel reaction is used to synthesize a triple perovskite with a composition Sr3Co2WO9 (SCWO). The structural analysis conducted at room temperature reveals the presence of the cubic phase with space group Fm-3m. The microstructure of the as-synthesized SCWO particles shows a different size of particles depicting a polycrystalline nature. Triboelectrification is a trending and unique concept in energy scavenging methodologies with flexibility in choosing from a variety of materials. This paves the way to evolve eco-friendly triboelectric energy harvesters as a replacement for the limitation of batteries. The outstanding dielectric properties and low loss make triple perovskite a promising candidate for TENG. A triboelectric nanogenerator (TP-TENG) was designed, which operates in vertical contact separation mode generating an electrical response of voltage and current of 300 V and 2.2 μA, respectively, for 10 wt% polydimethylsiloxane-Sr3Co2WO9 (PDMS-SCWO) composite film. The power density of the rough surface TP-TENG was 30.5 μW/cm2, which is much higher than the power density of 5.5 μW/cm2 of plain surface TP-TENG. The positive and negative triboelectric layers of the TP-TENG were made up of aluminum and PDMS-SCWO composite film, respectively. Furthermore, the excellent flexibility and durability of TP-TENG make it suitable for sensing various gaits and information signaling (Morse code) in real-time applications, as well as for charging commercial capacitors.

The main objective of this work was to synthesize phase pure double perovskites Ba2NiTeO6 (BNTO) and Ba2NiWO6 (BNWO) in nanocrystalline form and to reveal the impact of nanocrystallinity on their magnetic and dielectric properties. The studied double perovskites were synthesized in nanocrystalline form by employing a citrate sol-gel route. A detailed investigation of their structure and properties using X-ray powder diffraction, scanning electron microscopy, Raman spectroscopy technique, energy-dispersive X-ray spectroscopy, SQUID magnetometry and electrical measurements is carefully described. Rietveld refinement of X-ray powder diffraction patterns revealed phase purity of both compounds: BNTO is trigonal (R-3m) while BNWO is cubic (Fm-3m). Raman spectroscopy studies reveal optical phonons that correspond to vibrations of Te6+/W6+O6 octahedra, while scanning electron microscopy images show irregular plate-like nanocrystals. Magnetic property measurements speak in favor of antiferromagnetic order but, in both compounds, size reduction affected their properties. BNTO has Néel temperature (TN) of 10.3 K which is higher than previously reported for its bulk form. Magnetic ground state of BNWO can be explained as canted antiferromagnetism with TN = 48.2 K. Room temperature measurements of dielectric constants at various frequencies suggest that these materials are high-κ dielectrics with low dielectric loss. The Nyquist plot reveals depressed a semicircle arc typical for non-Debye type of relaxation phenomena for BNWO ceramic, whereas for BNTO ceramic an almost straight line of Zʹʹ versus Z' has been observed, indicating its high insulating behavior. To conclude, size-dependent properties of studied double perovskites are discussed, introducing a possibility for implementation in electronic devices.

Complex perovskites have attracted extensive attention due to their fascinating physical properties and novel features owing to the coexistence of the ferro/ferri-magnetic ground state and semiconducting behavior in the single material. Herein, the triple perovskite Sr3Co2WO9 (SCWO) has been successfully synthesized for the first time in the nanocrystalline form with an average crystallite size of 23 nm using a high yield (81 %) aqueous citrate sol-gel method. At room temperature, the crystal structure of Sr3Co2WO9 is cubic, space group Fm-3m, with lattice parameter a= 7.9073(6) Å. The formation of SCWO triple perovskite was studied in situ by X-ray diffraction and subsequently analyzed by the Rietveld analysis. The detected hysteresis loops with non-zero remanent magnetization and rather large coercive field reveal ferrimagnetic ordering with a Curie temperature of 144 K. The measured effective magnetic moment of 3 μB is close to the expected value for rarely observed intermediate spin S = 1. It is found that the compound exhibits semiconducting properties with the optical band gaps equal to 3.52 eV (indirect) and 3.76 eV (direct), respectively, further confirmed by the determination of the AC conductivity, which in the measured temperature range (25 -500 °C at 1 kHz) lies within the interval from 10−5- 10−4 Ω−1 cm−1. The Maxwell -Wagner model is employed to describe the frequency dependent dielectric constant. The frequency-dependent AC conductivity follows the universal Jonscher’s power law. Since it possesses both magnetic and semiconductor properties, this material could be a promising candidate to use in devices where its semiconducting properties would be spin-controlled.

In this study, three different precipitation systems of increasing complexities were used to study formation of calcium oxalate hydrates under hyperoxaluria conditions. For this purpose, three different precipitation systems have been studied: a) a simple system (a system containing constituent ions), b) NaCl system (a system consisted of constituent ions and 0.3 mol dm−3 NaCl), and c) artificial urine system (a system containing constituent ions that are of the type and quantity mimicking real urine) at initial pH (pHi = 6.5) value, with and without added vitamin C. The vitamin C has been extensively tested for its ability to inhibit or promote the process of calcium oxalate precipitation or the formation of specific hydrate modification. In order to determine whether calcium oxalate crystallization could be affected by the presence of vitamin C in precipitation systems with increasing complexity, different amounts of vitamin C (in the mass range from 100 mg to 1000 mg) were added to the precipitation systems.The results indicated that in all investigated simple systems, calcium oxalate monohydrate (COM) is observed to be dominant precipitated hydrate phase, while in NaCl systems precipitation of COM and calcium oxalate trihydrate (COT) mixture occurrs, except in reference NaCl system (without addition of vitamin C) where COM precipitated exclusively. In reference artificial urine system, calcium oxalate dihydrate (COD) was observed to be dominant precipitated hydrate phase, while addition of vitamin C promoted precipitation of COT. Significant differences are mainly observed in crystal morphology and the content of individual hydrate phases. Electrochemical measurements have indicated the existence of electrostatic interactions between seed crystals and ascorbic acid, even at low masses of added vitamin C.

Double perovskites have been extensively studied in materials chemistry due to their excellent properties and novel features attributed to the coexistence of ferro/ferri/antiferro-magnetic ground state and semiconductor band gap within the same material. Double perovskites with Sr2NiMO6 (M = Te, W) structure type have been synthesized using simple, non-toxic and costless aqueous citrate sol-gel route. The reaction yielded phase-pure nanocrystalline powders of two compounds: Sr2NiWO6 (SNWO) and Sr2NiTeO6 (SNTO). According to the Rietveld refinement of powder X-ray diffraction data at room temperature, Sr2NiWO6 is tetragonal (I4/m) and Sr2NiTeO6 is monoclinic (C12/m1), with average crystallite sizes of 49 and 77 nm, respectively. Structural studies have been additionally performed by Raman spectroscopy revealing optical phonons typical for vibrations of Te6+/W6+O6 octahedra. Both SNTO and SNWO possess high values of dielectric constants (341 and 308, respectively) with low dielectric loss (0.06 for SNWO) at a frequency of 1 kHz. These values decrease exponentially with the increase of frequency to 1000 kHz, with the dielectric constant being around 260 for both compounds and dielectric loss being 0.01 for SNWO and 0.04 for SNTO. The Nyquist plot for both samples confirms the non-Debye type of relaxation behavior and the dominance of shorter-range movement of charge carriers. Magnetic studies of both compounds revealed antiferromagnetic behavior, with N&eacute, el temperature (TN) being 57 K for SNWO and 35 K for SNTO.