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.

Site-occupancy scheme in disordered Ca3RE2(BO3)4: a dependence on rare-earth (RE) ionic radius.

The structures of polycrystalline Ca3RE2(BO3)4 (RE = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Y; space group Pnma) orthoborates were determined using powder X-ray diffraction. Trends in the unit-cell dimensions and yet unreported trends in other structural properties (interatomic distances and the fractional occupation of three Ca/RE sites) for these compounds are demonstrated as a function of RE ionic radius. The unit-cell volume and a unit-cell parameter present a linear dependence, while the b and c unit-cell parameters change in a nonlinear manner. For the whole series, the RE atoms are present at all three cationic sites (labelled as M1, M2 and M3), but the fractional occupancies depend on the RE ionic radius. The small rare-earth atoms tend to enter mainly the M3 site; for the larger rare earths, the occupancy of this site decreases sharply. The occupancy of the M1 site by RE atoms is around 0.5 and tends to increase with increasing RE ionic radius. The M2 site is the least preferentially occupied by RE ions, but the occupancy discernibly increases with rising radius as well. These findings are assembled with properties of isostructural strontium and barium borates, allowing prediction of occupancy schemes for not yet investigated compounds from the A3RE2(BO3)4 (A = Ca, Ba, Sr).

Vibrational and optical studies of a nonlinear optical crystal, Cs2Bi2O(Ge2O7).

Single crystals of a non-centrosymmetric and polar Cs2Bi2O(Ge2O7) compound were grown from melt. This material was characterized by polarized Raman scattering at room temperature. The comparison to the polycrystalline IR and Raman spectra has been made and assignment of all observed modes to the respective vibrations and their symmetry has been proposed. Our results show that this crystal is promising SRS-active nonlinear optical material for up- and down-Raman laser-frequency converters with the most intense lasing line at 481 cm-1. Optical studies show that Cs2Bi2O(Ge2O7) exhibits intense absorption bands with peaks maxima at 260 and 293 nm (77 K) typical for 1S0→1,3P1 transitions of Bi3+ ions, which are parity-allowed due to spin-orbit coupling as well as unexpected band centered at 360 nm that was assigned to intervalence charge transfer transition.

Enhanced 1.5 µm emission of Er3+-doped multifunctional Bi2ZnOB2O6 microcrystals.

The efficiency of the 1.5 µm emission associated with the 4I13/2 → 4I15/2 transition of Er3+ ions of a series of Er3+ and Yb3+/Er3+-doped Bi2ZnOB2O6 microcrystalline powders was investigated. Bi2ZnOB2O6 is an excellent nonlinear optical material as well as a good host matrix for luminescent rare-earth ions. The investigated powders were synthesized by means of the modified Pechini method and their orthorhombic structure with Pba2 space group were confirmed by XRD measurements. The vibrational properties of Bi2ZnOB2O6:Yb3+/Er3+ were studied using µ-Raman spectroscopy. The low phonon energy of the Bi2ZnOB2O6 matrix allows effective phonon assisted energy transfer between rare-earth ions and/or multiphonon relaxation processes of rare-earth ions. It was revealed that the intensity of the 1.5 µm emission under 980 nm excitation increased with increasing Er3+ concentration (from 0.5 to 3.0 at%) for Bi2ZnOB2O6:Er3+, while for co-doped Bi2ZnOB2O6:Yb3+/Er3+ systems a significant increase in this emission was observed for the optimal Yb3+/Er3+ concentration (1.5/0.5 at%). Moreover, the intensity of the 1.5 µm emission decreases with increasing temperature for all investigated samples. Additionally, Bi2ZnOB2O6:Yb3+/Er3+ powders exhibit effective up-conversion luminescence in the visible range under 980 nm excitation. In the up-conversion spectra of Bi2ZnOB2O6:Yb3+/Er3+ powders, the bands corresponding to green and red emission of Er3+ ions (2H11/2 → 4I15/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively), as well as the bands at about 487 nm (blue emission) associated with second harmonic generation produced by the Bi2ZnOB2O6 matrix were detected. The results indicate a potential for application of Bi2ZnOB2O6:Yb3+/Er3+ powders as effective multifunctional new-generation photonic materials.

The effect of dopant chirality on the properties of self-assembling materials with a ferroelectric order.

A series of achiral hockey stick-shaped molecules forming a tilted smectic I liquid crystal phase as well as one non-mesogenic chiral bistereogenic analogue were synthesized and characterized. Herein, we report an example of an achiral hockey stick-shaped compound exhibiting a smectic I phase with a direct transition to the isotropic phase for the first time. This occurrence was confirmed via polarized light microscopy, dielectric spectroscopy, and XRD studies. Homologues with an odd number of carbon atoms in the oligomethylene spacer chain exhibit a lower clearing point than members posessing an even number of carbon atoms in this chain; thus, a characteristic odd-even effect has been observed. The influence of the synthesized compounds with different degrees of chirality and similar chemical structures on the properties of the host compound with a chiral smectic C phase was investigated. A chiral compound forming a wide-temperature chiral smectic C phase without any additional mesophase and having a short helical pitch was selected as the host material for the creation of two bicomponent systems. The mesomorphism of each binary mixture was characterized using optical microscopy and differential scanning calorimetry. The helical pitch of every binary mixture, forming a chiral smectic C phase, was studied within its full phase temperature range. As expected, the chiral host compound in the smectic C* phase doped with the hockey stick-shaped mesogen exhibited a longer helical pitch and lower spontaneous polarization than the chiral host material. On the other hand, for the chiral host compound doped with a non-mesogenic analogue containing two chiral centres, the helical pitch was shorter, and the spontaneous polarization was higher. These results should be potentially applicable for the design of advanced functional multi-component mixtures useful for various applications. The mesogenic behaviour of one binary mixture, forming both the chiral smectic I and titled chiral smectic C phases, was deeply studied via X-ray diffraction and dielectric spectroscopy techniques.