THE INFLUENCE OF SINGLY CHARGED IONS ON THE TRANSLATIONAL MOTION OF MOLECULES IN EXTREMELY DILUTE AMIDE SOLUTIONS

The type of short range solvation of Li+, Na+ K+, Rb+, Cs+, NH4+, Cl– , Br–, I–, ClO4– ions has been determined and analyzed in formamide (FA), N-methylformamide (MFA), N-dimethylformamide (DMF) at 298.15 K. In order to determine the type of ion solvation we used familiar-variable quantitative parameter (– ri), where is the translational displacement length of ion, ri is its structural radius. It was found that the difference (– ri) is equal to the coefficient of attraction friction (CAF) of ions normalized to the solvent viscosity and hydrodynamic coefficient. The sign of the CAF is determined by the sign of the algebraic sum of its ion-molecular and intermolecular components. In amide solutions the studied cations are cosmotropes (positively solvated ((– ri) > 0), structure-making ions) and anions are chaotropes (negatively solvated ((– ri) < 0 ), structure-breaking ions). In the amide series, regardless of the sign (– ri), the near-solvation enhances, which can be explained by the weakening of the specific interaction between the solvent molecules. The decrease of and respectively (– ri) with increasing cation radius in a given solvent is the result of weakening of its coordinating force due to the decrease of charge density in the series Li+–Na+–K+–Rb+–Cs+. The increase of (and (– ri), correspondingly) for the ions studied in the series FA- MFA-DMF can be explained by the weakening of intermolecular interactions in this series, which leads to the strengthening of solvation. It was found that for the halide ions in the series FA-MFA-DMF the regular growth of parameter is explained by the weakening of the solvent structure. It was shown that Li+ ion with the lowest diffusion coefficient among cations and the highest value forms kinetically stable complexes in amide solutions.

Spin-Phonon Coupling in A2BMnO6 (A = La, Pr, Nd, Sm, Gd; B = Co, Ni) Double-Perovskite Thin Films: Impact of the A-Site Cation Radius

Two series of B-site ordered, double-perovskite A2CoMnO6 and A2NiMnO6 (A = La, Pr, Nd, Sm, Gd) epitaxial films with thickness d ~ 100 nm were grown on SrTiO3(111) substrates via metalorganic aerosol deposition. Polarization and temperature-dependent Raman spectroscopy were carried out in order to determine the spin-phonon coupling constant, λ, and the impact of the A-site cation radius on the phonon properties. The reduction of the A-site cation radius from La3+ down to Gd3+ systematically shifts the Raman modes to lower wavenumbers, and decreases the magnetization-induced softening of the Ag breathing mode, described by the spin-phonon coupling constant, λ, which changes from λ = 1.42 cm−1 (La2CoMnO6) and λ = 1.53 cm−1 (La2NiMnO6) down to λ = 0.58 cm−1 (Gd2CoMnO6) and λ = 0.44 cm−1 (Gd2NiMnO6). A similar effect of the A-cation radius was established for the c-lattice parameter and Curie temperature, TC, in this series of double-perovskite films. Our observations directly demonstrate a strong impact of the lattice structure on the ferromagnetic superexchange interaction in double perovskites. Moreover, the A2CoMnO6 and A2NiMnO6 series exhibit very similar behavior of spin-phonon coupling due to the only moderate difference of Co2+ and Ni2+ cation size.

Comprehensive Density Functional Theory Studies of Vibrational Spectra of Carbonates

Within the framework of the density functional theory (DFT) and the hybrid functional B3LYP by means of the CRYSTAL17 program code, the wavenumbers and intensities of normal oscillations of MgCO3, CaCO3, ZnCO3, CdCO3 in the structure of calcite; CaMg(CO3)2, CdMg(CO3)2, CaMn(CO3)2, CaZn(CO3)2 in the structure of dolomite; BaMg(CO3)2 in the structure of the norsethite type; and CaCO3, SrCO3, BaCO3, and PbCO3 in the structure of aragonite were calculated. Infrared absorption and Raman spectra were compared with the known experimental data of synthetic and natural crystals. For lattice and intramolecular modes, linear dependences on the radius and mass of the metal cation are established. The obtained dependences have predictive power and can be used to study solid carbonate solutions. For trigonal and orthorhombic carbonates, the linear dependence of wavenumbers on the cation radius RM (or M–O distance) is established for the infrared in-plane bending mode: 786.2–65.88·RM and Raman in-plane stretching mode: 768.5–53.24·RM, with a correlation coefficient of 0.87.

Structure and diffusion of molten alkali carbonate salts at the liquid-vacuum interface

The liquid-vacuum interface of molten alkali carbonate salts is studied with molecular dynamics simulations. Three salts comprised of LixNayKzCO3 near their respective eutectic concentrations are considered to understand the distribution of ions relative to a liquid-vacuum interface and their diffusivity. These simulations show that each of the cations accumulate at the interface preferentially compared to carbonate. The cation ordering is found to inversely correspond to cation radius, with K being the most likely occupant at the surface, followed by Na, Li, and then the anion. Similar to other studies, the carbonate is found to diffuse more slowly than the cations, but we do observe small differences in diffusion between compositions that present opportunities to optimize ion transport. These results hold consequences for our understanding of ion behavior in molten carbonate salts and the performance of devices employ these electrolytes.

Limits of Cation Solubility in AMg2Sb2 (A = Mg, Ca, Sr, Ba) Alloys

A M 2 X 2 compounds that crystallize in the CaAl 2 Si 2 structure type have emerged as a promising class of n- and p-type thermoelectric materials. Alloying on the cation (A) site is a frequently used approach to optimize the thermoelectric transport properties of A M 2 X 2 compounds, and complete solid solubility has been reported for many combinations of cations. In the present study, we investigate the phase stability of the AMg 2 Sb 2 system with mixed occupancy of Mg, Ca, Sr, or Ba on the cation (A) site. We show that the small ionic radius of Mg 2 + leads to limited solubility when alloyed with larger cations such as Sr or Ba. Phase separation observed in such cases indicates a eutectic-like phase diagram. By combining these results with prior alloying studies, we establish an upper limit for cation radius mismatch in A M 2 X 2 alloys to provide general guidance for future alloying and doping studies.

Spectral Properties and Thermal Quenching of Mn-=SUP=-4+-=/SUP=- Luminescence in Silicate Garnet Hosts CaY-=SUB=-2-=/SUB=-MgMAlSi-=SUB=-2-=/SUB=-O-=SUB=-12-=/SUB=- (M=Al, Ga, Sc) -=SUP=-*-=/SUP=-

Multi-component silicate garnet ceramics CaY_2MgMAlSi_2O_12 comprising different cations M = Al, Ga or Sc in octahedral sites doped with Mn^4+ ions have been synthesized and studied as novel red-emitting phosphors aiming at warm white pc -LED applications. All synthesized phosphors exhibit Mn^4+ luminescence in rather deep red region, the shortest-wavelength spectrum of Mn^4+ luminescence (peak wavelength at 668 nm) being obtained for the host with the largest cation M^3+ = Sc^3+ in the octahedral site. The effect of increasing the energy of the emitting Mn^4+^2 E level with the size of the host cation in octahedral sites is supposed to be the result of decrease of the covalence of the “Mn^4+-ligand” bonding with increase of the interionic Mn^4+–O^2– distance. All studied phosphors demonstrate rather poor thermal stability of Mn^4+ photoluminescence with a thermal quenching temperature T _1/2 below 200 K, the lowest value being observed for the host with M = Sc. As expected, the decrease of the energy of the O^2––Mn^4+ charge-transfer state is observed with the increase of the M^3+ cation radius, i.e. with the increase of the O^2––Mn^4+ interionic distance. The thermal quenching temperature of Mn^4+ luminescence in the studied phosphors correlates with the energy of the O^2––Mn^4+ charge transfer state which is supposed to serve as a quenching state for Mn^4+ luminescence.

Nanodomains and local structure in ternary alkaline-earth hexaborides

The local structures of ternary alkaline-earth hexaborides (MB6, M = Ca0.5Sr0.5, Ca0.5Ba0.5 and Sr0.5Ba0.5) have been analysed using X-ray pair distribution function (PDF) analysis, Raman spectroscopy and transmission electron microscopy (TEM). The results show significant local deviations from the average cubic structure within the boron sub-lattice and support the conclusion that rapid synthesis processes lead to the formation of coherent nanodomains over length scales of about 10 nm. Reverse Monte Carlo fitting of the PDFs allows for quantification of the displacement disorder within the boron sub-lattice as a function of sample composition. Detailed Raman spectroscopy studies and high-resolution TEM support the models derived from X-ray scattering. The average magnitude of the static displacement disorder varies by sample composition and positively correlates with the cation radius ratios across the three compositions. The new models form a foundation for future computational and experimental studies aimed at understanding and predicting properties of hexaborides.

Different coordination modes of trans-2-{[(2-methoxyphenyl)imino]methyl}phenoxide in rare-earth complexes: influence of the metal cation radius and the number of ligands on steric congestion and ligand coordination modes

A simple and effective synthetic route to homo- and heteroleptic rare-earth (Ln = Y, La and Nd) complexes with a tridentate Schiff base anion has been demonstrated using exchange reactions of rare-earth chlorides with in-situ-generated sodium (E)-2-{[(2-methoxyphenyl)imino]methyl}phenoxide in different molar ratios in absolute methanol. Five crystal structures have been determined and studied, namely tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ3 O 1,N,O 2)lanthanum, [La(C14H12NO2)3], (1), tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato-κ3 O 1,N,O 2)neodymium tetrahydrofuran disolvate, [La(C14H12NO2)3]·2C4H8O, (2)·2THF, tris(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-κ3 O 1,N,O 2;κ3 O 1,N,O 2;κ2 N,O 1-yttrium, [Y(C14H12NO2)3], (3), dichlorido-1κCl,2κCl-μ-methanolato-1:2κ2 O:O-methanol-2κO-(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κ3 O 1,N,O 2:2κO 1)bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato)-1κ3 O 1,N,O 2;2κ3 O 1,N,O 2-diyttrium–tetrahydrofuran–methanol (1/1/1), [Y2(C14H12NO2)3(CH3O)Cl2(CH4O)]·CH4O·C4H8O, (4)·MeOH·THF, and bis(μ-2-{[(2-methoxyphenyl)imino]methyl}phenolato-1κ3 O 1,N,O 2:2κO 1)bis(2-{[(2-methoxyphenyl)imino]methyl}phenolato-2κ3 O 1,N,O 2)sodiumyttrium chloroform disolvate, [NaY(C14H12NO2)4]·2CHCl3, (5)·2CHCl3. Structural peculiarities of homoleptic tris(iminophenoxide)s (1)–(3), binuclear tris(iminophenoxide) (4) and homoleptic ate tetrakis(iminophenoxide) (5) are discussed. The nonflat Schiff base ligand displays μ2-κ3 O 1,N,O 2:κO 1 bridging, and κ3 O 1,N,O 2 and κ2 N,O 1 terminal coordination modes, depending on steric congestion, which in turn depends on the ionic radii of the rare-earth metals and the number of coordinated ligands. It has been demonstrated that interligand dihedral angles of the phenoxide ligand are convenient for comparing steric hindrance in complexes. (4)·MeOH has a flat Y2O2 rhomboid core and exhibits both inter- and intramolecular MeO—H...Cl hydrogen bonding. Catalytic systems based on complexes (1)–(3) and (5) have demonstrated medium catalytic performance in acrylonitrile polymerization, providing polyacrylonitrile samples with narrow polydispersity.

New Mixed Y0.5R0.5VO4 and RVO4:Bi Materials: Synthesis, Crystal Structure and Some Luminescence Properties

The results are reported on a precise crystal structure and microstructure determination of new mixed YVO4-based orthovanadates of Y0.5R0.5VO4 (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) as well as some Bi3+-doped RVO4 (R = La, Gd, Y, Lu) nano- (submicro-) materials. The formation of continuous solid solutions in the YVO4–RVO4 pseudo-binary systems (R = Sm, Tb, Dy, Ho, Tm, Yb, Lu) has been proved. The lattice constants and unit cell volumes of the new mixed orthovanadates were analyzed as a function of R3+ cation radius. The impact of crystal structure parameters on the energy band gap of the materials was studied by means of photoluminescence studies of the Bi3+-doped compounds.

CATIONIC CONDUCTIVITY IN MIXED POLYFERRITES

The effect of chemical composition on the cationic conductivity of mixed alkali metals β"-polyferrites was established. Cationic conductivity is determined by the mobility of alkali metal ion in inter-unit space which in turn depends on the ratio of cation radius and width of inter-unit space. The conductivity increases with z, and at the same z in the range of 0.28 – 0.4 becomes constant (z in the formula Me2-zAdzFe11O17, where Me - the basic alkali metal, Ad - introduced alkali metal ion, which has the larger radius (Cs, Rb)) for all samples. This is due to the structural features of polyferrites.