Synthesis and Properties of the Ba2PrWO6 Double Perovskite.

We report details on the synthesis and properties of barium praseodymium tungstate, Ba2PrWO6, a double perovskite that has not been synthesized before. Room-temperature (RT) powder X-ray diffraction identified the most probable space group (SG) as monoclinic I2/m, but it was only slightly distorted from the cubic structure. X-ray photoelectron spectroscopy confirmed that the initial (postsynthesis) material contained praseodymium in both 3+ and 4+ charge states. The former (Pr3+) disappeared after exposure to UV light at RT. Photoluminescence studies of Pr3+ revealed that Ba2PrWO6 is an insulator with a band gap exceeding 4.93 eV. Pressure-dependent Raman spectroscopy excluded the possibility of a phase transition up to 20 GPa; however, measurements between 8 and 873 K signified that there might be a change toward the lower symmetry SG below 200 K. Electron paramagnetic resonance spectra revealed the presence of interstitial oxygen which acts as a deep electron trap.

Correction to "Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions".

[This corrects the article DOI: 10.1021/acsomega.2c00669.].

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions.

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium-tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A2BB'X6 group of compounds contains mainly divalent alkali cations in the form of XIIA = Ba2+, Ca2+ sharing, here, oxygen-arranged clusters (IIX = O2-) with purposely selected central ions from f-block VIB = Ce4/3+ and d-block VIB' = W4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material's unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Carbon and Manganese in Semi-Insulating Bulk GaN Crystals.

Co-doping with manganese and carbon was performed in gallium nitride grown by halide vapor phase epitaxy method. Native seeds of high structural quality were used. The crystallized material was examined in terms of its structural, optical, and electrical properties. For that purpose, different characterization methods: x-ray diffraction, Raman spectroscopy, low-temperature photoluminescence, and temperature-dependent Hall effect measurements, were applied. The physical properties of the co-doped samples were compared with the properties of crystals grown in the same reactor, on similar seeds, but doped only with manganese or carbon. A comparison of the electrical and optical properties allowed to determine the role of manganese and carbon in doped and co-doped gallium nitride crystals.

High-Pressure Low-Temperature Optical Studies of BaWO4:Ce,Na Crystals.

We report detailed optical studies of BaWO4:Ce and BaWO4:Ce,Na single crystals. The material does not emit any luminescence at ambient pressure under near-UV (325 nm) excitation. Efficient green light is emitted only at high pressure (HP) and low temperature (LT). The luminescence is of excitonic character, since the lowest Ce3+ 5d level is degenerate with the conduction band also under hydrostatic pressures. To explain these phenomena, absorption measurements were made together with powder X-ray diffraction (XRD) and confocal micro-Raman and Fourier transform infrared (FTIR) spectroscopy. Raman experiments confirm the existence of a metastable phase, induced by certain nonhydrostatic conditions, before the reversible transition at a high-pressure range above 9 GPa, where efficient photoluminescence (PL) occurs. Although the phase transition is reversible, it proceeds with a prominent hysteresis observed in luminescence and Raman experiments. FTIR focuses on the existence of Ce3+ multisites observed during LT measurements.

Equation of State and Amorphization of Ca9R(VO4)7 (R = La, Nd, Gd): A Combined High-Pressure X-ray Diffraction and Raman Spectroscopy Study.

Ca9R(VO4)7 (R = rare earth) multicomponent oxides of a whitlockite-related structure are under consideration for applications in optoelectronics. In this work, the Czochralski-grown Ca9R(VO4)7 crystals were investigated as a function of pressure by powder X-ray diffraction and single-crystal Raman spectroscopy. The diffraction experiments were performed at the ALBA synchrotron under pressures ranging up to 9.22(5), 10.7(1), and 8.55(5) GPa for R = La, Nd, and Gd, respectively, to determine the third order equation of state (EOS) parameters. Fitting of the Birch-Murnaghan EOS provided the isothermal bulk moduli K0 = 63(4), 63(2), and 61(5) GPa for these three orthovanadates. These values are apparently lower than that reported for structurally related tricalcium vanadate Ca3(VO4)2. The compressibility anisotropy was observed; the lattice is markedly stiffer in [001] than in [100] direction. For Ca9Nd(VO4)7, the variation of the diffractograms just above 10 GPa provides an indication on the beginning of amorphization process; during pressure release the whitlockite-like structure is recovered. Raman spectroscopy measurements for single crystals of the above-mentioned rare-earth vanadates and Ca9Y(VO4)7 were performed (the maximum pressures achieved were 16.3(1), 21.2(1), 15.3(1), and 18.6(1) GPa for R = Y, La, Nd, and Gd, respectively). These measurements reveal a partially reversible phase transition interpreted as amorphization, with an onset at the pressure of ∼9-10 GPa, characterized by broadening of the peaks and their shift to lower energies.

The Influence of Calcium Glycerophosphate (GPCa) Modifier on Physicochemical, Mechanical, and Biological Performance of Polyurethanes Applicable as Biomaterials for Bone Tissue Scaffolds Fabrication.

In this paper we describe the synthesis of poly(ester ether urethane)s (PEEURs) by using selected raw materials to reach a biocompatible polyurethane (PU) for biomedical applications. PEEURs were synthesized by using aliphatic 1,6-hexamethylene diisocyanate (HDI), poly(ethylene glycol) (PEG), α,ω-dihydroxy(ethylene-butylene adipate) (Polios), 1,4-butanediol (BDO) as a chain extender and calcium glycerolphosphate salt (GPCa) as a modifier used to stimulate bone tissue regeneration. The obtained unmodified (PURs) and modified with GPCa (PURs-M) PEEURs were studied by various techniques. It was confirmed that urethane prepolymer reacts with GPCa modifier. Further analysis of the obtained PURs and PURs-M by Fourier transform infrared (FTIR) and Raman spectroscopy revealed the chemical composition typical for PUs by the confirmed presence of urethane bonds. Moreover, the FTIR and Raman spectra indicated that GPCa was incorporated into the main PU chain at least at one-side. The scanning electron microscopy (SEM) analysis of the PURs-M surface was in good agreement with the FTIR and Raman analysis due to the fact that inclusions were observed only at 20% of its surface, which were related to the non-reacted GPCa enclosed in the PUR matrix as filler. Further studies of hydrophilicity, mechanical properties, biocompatibility, short term-interactions, and calcification study lead to the final conclusion that the obtained PURs-M may by suitable candidate material for further scaffold fabrication. Scaffolds were prepared by the solvent casting/particulate leaching technique (SC/PL) combined with thermally-induced phase separation (TIPS). Such porous scaffolds had satisfactory pore sizes (36⁻100 µm) and porosity (77⁻82%) so as to be considered as suitable templates for bone tissue regeneration.