Indication from NMR of Grotthuss mechanism for proton conduction in H2Sb4O11·nH2O

We have measured the second moment, the linewidth and the relaxation times T₁ and T₂ of the ¹H magnetic resonance signal from 4.2 to 380 K in the fact proton conductors H₂Sb₄O₁₁·nH₂O. Our results reveal that the high ionic conductivity of these materials is due to a Grotthuss-type proton diffusion mechanism with succession of molecular reorientations of H₃O⁺ ions or H₂O molecules and of proton jumps from H₃O⁺ to H₂O.     

Formation and lithuim ionic conduction of the antifluorite type solid electrolytes,Li2+x-y-z[(NH)1-x-y-zNxClyHz]

Antifluorite type solid electrolytes, Li_2+x-y-z[(NH)_1-x-y-zN_xCl_yH_z] have been synthesized from Li₃N, LiCl and LiCl·H₂O or $\text{Li}{}_2\text{[(}\text{NH}\text{)}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{H}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$]. Either of the last two compounds introduces NH^2- ions into the product and is indispensable to form the antifluorite type structure. The lattice parameter decreases with increasing amount of NH^2- ions in the compound, reflecting the difference of anion sizes between Cl^- and NH^2- ions. Activation energies of Li⁺ diffusive motion, derived from both conductivity and NMR measurements, increase with concentration of NH^2- ions, although the values differ by a factor of ≈2 netween the both methods.     

Dielectric, ferroelectric and pyroelectric properties of Pb[(Ni1/3Sb2/3)xTiyZrz]O3 ceramics

In the present study, various Pb[(Ni_1/3Sb_2/3)_xTi_yZr_z]O₃ where x+y+z=1, x=0.08 and y=0.44-0.49, ceramics in the morphotropic phase boundary (MPB) range were studied by dielectric and pyroelectric methods. The results of the investigations revealed an MPB composition range of y≅0.46. The study of the dielectric properties of these compounds as a function of temperature suggests that with increase in y the permittivity maximum increases and transition temperature shifts towards higher temperature. Well-saturated polarization versus electric field (P-E) hysteresis loops were obtained and values of P_r were calculated. The samples revealed good pyroelectric properties for y=0.44 and y=0.45 at room temperature with large figures of merit F_v=0.019 m²/C and F_D=1.34×10^-5Pa^1/2.     

Vibrational study of H3OUO2PO4·3 H2O (HUP) and related compounds. Phase transitions and conductivity mechanism: Part II,H3OUO2PO4·3 H2O

Infrared and Raman spectra of polycrystalline H₃OUO₂PO₄·3 H₂O (HUP) and its D and P¹⁸O₄ derivatives, in the form of dense transparent disks and wet powder, have been investigated at various temperatures in the 100–300 K region. The bands due to framework vibrations are similar to those of KUP, whereas those for the protonic species are different. OH stretching and bending bands of the oxonium ion have been identified at 2920, 1740 and 1160 cm^?1 in the low-temperature spectrum of HUP. Differential scanning calorimetry (DSC) and infrared (IR) intensity investigations show a phase transition between 274 and 260 K. The mechanism of the phase transition consists, as in the case of KUP, of ordering of the protonic species, which induces ordering of PO₄ tetrahedra. The ordering can be influenced by excess water content, stacking faults and stress (ferroelastic behaviour is evidenced). The conductivity mechanism in HUP is discussed.     

Estimation of T1 for Co2+ ions from the temperature variation of the ESR linewidths for VO2+ in Cs2Co(SeO4)2·6H2O single crystals

The electron spin resonance of VO²⁺ is studied in single crystals of Cs₂M″ (SeO₄)₂·6H₂O (M″ = Zn, Co) from 290 to 77 K at ～ 9.45 GHz. The line broadening of VO²⁺ spectra on cooling the Cs₂Co(SeO₄)₂·6H₂O crystal is explained on the basis of host spin-lattice relaxation narrowing. T₁ for Co²⁺ is estimated to be ≈ 1.7 × 10^?12 sec. at 290 K.     

Experimental and Theoretical Study of Hydrogen Atom Abstraction from C2H6 and C4H10 by Zirconium Oxide Clusters Anions

使用配有团簇产生和化学反应源的飞行时间质谱装置,研究了锆氧阴离子团簇Zr_xOy^-与乙烷和丁烷的反应. 在反应中发现了Zr₂O₅H^-和Zr₃O₇H^-产物. 用密度泛函理论研究了乙烷在Zr₂O₅^-上的反应通道,发现乙烷脱氢反应可以发生,从而证明观察到的产物是源于脱氢反应. 该工作揭示了锆氧负离子团簇与烷烃反应中的新通道.     

Enhanced luminescence of Ca3B2O6:Dy phosphors by Na-codoping for LED applications

The Ca_2.95−yDy_0.05B₂O₆:yNa⁺ (0≤y≤0.20) phosphors were synthesized at 1100 °C in air by the solid-state reaction route. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), photoluminescence excitation (PLE), photoluminescence (PL) spectra and thermoluminescence (TL) spectra. The PLE spectra show the excitation peaks from 300 to 400 nm due to the 4f-4f transitions of Dy³⁺. This mercury-free excitation is useful for solid-state lighting and light-emitting diodes (LEDs). The emission of Dy³⁺ ions on 350 nm excitation was observed at 480 nm (blue) due to the ⁴F_9/2→⁶H_15/2 transitions, 575 nm (yellow) due to ⁴F_9/2→⁶H_13/2 transitions and 660 nm (red) due to weak ⁴F_9/2→⁶H_11/2 emissions. The PL results from the investigated Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors show that Dy³⁺ emissions increase with the increase of the Na⁺ codoping ions. The integral intensity of yellow to blue (Y/B) can be tuned by controlling Na⁺ content. By the simulation of white light, the optimal CIE value (0.328, 0.334) can be achieved when the content of Na⁺-codoping ions is y=0.2. The results imply that the Ca_2.95−yDy_0.05B₂O₆:yNa⁺ phosphors could be potentially used as white LEDs.     

The spin glass-like behaviour of the glassy (Sb2S3)x(SbI3)yFez

Low field magnetic susceptibility of a glassy semiconductor (Sb₂S₃)_x(SbI₃)_yFe_z reveals a spin glass-like behaviour in spite of the sample not being metallic. The critical temperature is observed to depend on the concentration of the iron atoms (T_M = 0.179z^0.76).     

Features of the local structure of hydrated fluorine-substituted solid solutions based on Ba2In2O5

It is found for hydrated solid solutions of Ba_2?0.5x In₂O_5?x F _x · nH₂O, Ba₂In₂O_5?0.5y F _y · nH₂O (0 ≤ x ≤ 0.30; 0 ≤ y ≤ 0.24) that increasing the concentration of fluorine lowers the degree of hydration. The composition of proton-containing groups and the places of their localization in the structure of hydrated oxyfluorides are determined. The presence of fluorine in the complex oxide’s structure helps increase the mobility of protons.     

Etude par effet Mössbauer de la structure hyperfine nucleaire de 121Sb dans Fe2O3α

Samples of α-Fe₂O₃ containing antimony impurities have been investigated with the ¹²¹Sb Mössbauer effect.The ¹²¹Sb⁵⁺ impurity parameters were compared with those recently obtained for ¹¹⁹Sn⁴⁺ in α-Fe₂O₃. The observed increase of the H(0) value may be related to the greater electronic population of the 5s-orbitals in the case of Sb⁵⁺ doping.     

EPR observation of a high temperature phase transition in Zn(ClO4)2·6H2O:Mn2+

The electron paramagnetic resonance of Mn²⁺ doped in single crystals of Zn(ClO₄)₂·6H₂O has been studied at X-band in the temperature range 300–380 K. A phase transition, observed at ～ 346 K, is reported for the first time.     

Champs hyperfins magnetiques sur les noyaux de 121Sb5+ dans Cr2O3

The magnetic hyperfine interactions of the impurity Sb⁵⁺ in Cr₂O₃ have been examined by the Mössbauer effect of ¹²¹Sb.The magnetic field on the nucleus of ¹²¹Sb⁵⁺ (Cr₂O₃) measured at 77° K, H(0) = 170 ± 15 koe.The comparison of the results obtained for the impurity ¹²¹Sb⁵⁺ with those for the ¹¹⁹Sn⁴⁺ ions, occuring in the same matrix, suggests the preponderant effect of the decoupling of the electron spins of 5s valency on the values of the internal fields observed for those ions.     

Magnetic anisotropy and saturation of LaFe12O19 and some related compounds

The saturation magnetization σ_s and uniaxial anisotropy constants K₁ and K₂ are measured on a polycrystalline, crystal-oriented sample of LaFe₁₂O₁₉ contaminated with known amounts of Fe₃O₄ and LaFeO₃. K₁ and K₂ increase strongly with decreasing temperature and the value of K₁ = (19–24) × 10⁵ erg/g at T = 0 shows that the substance is considerably more anisotropic than BaFe₁₂O₁₉ (K₁ ? 8·5 × 10⁵ erg/g) at low temperatures. The σ_s-T curve is more convex than that of BaFe₁₂O₁₉, so that σ_s is 11 per cent higher at room temperature but lower at T = 0. The value σ_s(T = 0) = 96·2 G cm³/g (19·2 μ_B/molecule) and the anisotropic behaviour are attributed to the presence of 1 Fe²⁺/molecule occupying the octahedral 2a sites in the magnetoplumbite lattice and having a uniaxial anisotropy of 10–15 cm^?1/ion.From measurements on polycrystalline, crystal-oriented samples of BaFe_10·8Fe²⁺_0·6Ti⁴⁺_0·6O₁₉ and BaFe_10·5Fe²⁺_1·0Sb⁵⁺_0·5O₁₉ it was found that, in comparison with LaFe₁₁Fe²⁺O₁₉, σ_s (T = 0) is smaller and K₁ is much smaller and much less temperature-dependent. The difference in anisotropic behaviour is attributed to a different distribution of the Fe²⁺ ions among the lattice sites due to the effective positive charge of the Ti⁴⁺ and Sb⁵⁺ ions.     

Reactivity and XAFS study on (1−x)CeO2-xNiO (x=0.025-0.3) system in the two-step water-splitting reaction for solar H2 production

The redox reaction of Ce⁴⁺-Ce³⁺ promoted by the catalytic function of nickel ions in a (1−x)CeO₂-xNiO solid solution was investigated for solar H₂ production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O₂-releasing reaction with (1−x)CeO₂-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H₂ gas evolved by the reduced form were 1.2-2.5 cm³/g and the evolved gases amounts ratio of H₂/O₂ was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H₂O=H₂+1/2O₂). The maximum amounts of evolved H₂ and O₂ gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO₂-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O₂-releasing and H₂-generation reactions with (1−x)CeO₂-xNiO solid solution were repeatable with the redox system of Ce⁴⁺-Ce³⁺, which was enhanced by the catalytic function of Ni²⁺-Ni⁰.     

Evidence for the fröhlich collective mode in the one-dimensional conductor K2[Pt(CN)4] Br0.3 · 3H2O from far infrared reflection

Far infrared and infrared reflection measurements on single crystals of the one dimensional conductor K₂[Pt(CN)₄] Br_0.3 · 3H₂O have been performed at 4.2K, 62K and 300K for light polarized parallel (E6z) and perpendicular (E ? z) to the platinum chains. At 4.2K and 62K a strong structure is observed in the E6z spectrum near 40 cm^-1 which is not observable at 300K. This structure is interpreted as due to the Fröhlich collective 2q_F-phonon mode.     

Rigid lattice NMR spectra of proton conductors H(H2O)nSbO3

The “rigid lattice” ¹H NMR spectra of H(H₂O)_nSbO₃ have been interpreted for n=0.20, 0.92 and 1. For n?0.92 the compounds contain deformed H₃O⁺ ions and OH groups. For n=1 the real formula is (H₃O)_0.7H_0.3SbO₃,0.3 H₂O. The results are discussed in relation to the level of proton conductivity.     

The piezoelectric effect in Pb[(Fe1/3Sb2/3) x Ti y Zr z ]O3 ceramics

The piezoelectric properties of Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ with x + y + z = 1, x = 0.1, y = 0.43–0.48 ceramics have been investigated over a broad temperature range using a resonance technique. The influence of modification of PZT normal ferroelectric synthesized near the morphotropic phase boundary by a relaxor Pb(Fe_1/3Sb_2/3)O₃ compound on its physical properties was studied. The coefficients s ₁₁, k ₃₁, and d ₃₁ were calculated from the parameters characterizing the behavior of damped harmonic oscillator in the vicinity of the piezoelectric resonance. Several anomalies of the piezoelectric coefficients have been found in the temperature range 300–600 K. Two diffuse phase transitions were observed in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃. The anomaly near 530 K for y = 0.43 is responsible for the transition from the rhombohedral phase to the tetragonal one. For y > 0.44 this transition is found to be very diffuse and the coexistence of rhombohedral and tetragonal phases occurs. The observation of low piezoelectric activity confirms the existence of polar regions in Pb[(Fe_1/3Sb_2/3) _x Ti _y Zr _z ]O₃ above T _m.     

Vibrational study of H3OUO2PO4 · 3 H2O (HUP) and related compounds. phase transitions and conductivity mechanisms: part I,KUO2PO4 · 3 H2O (KUP)

Infrared and Raman spectra of polycrystalline KUO₂PO₄ · 3 H₂O (KUP) and its isotopic derivatives KUO₂P¹⁸O₄ · 3 H₂O and KUO₂PO₄ · 3 D₂O have been investigated in the 4000-10-cm^?1 range at different temperatures. An assignment of the bands in terms of UO₂, PO₄ and H₂O vibrations has been proposed. Combined differential scanning calorimetry and spectroscopic data show two diffuse phase transitions near 130 and 230 K. Comparison of the vibrational spectra of phase I at 300 K and phase IV at 100 K indicates that ordering of the water molecules with subsequent ordering of PO₄ tetrahedra on a site with lower symmetry appears to be the main mechanism responsible for the phase transformation. All the six O-H distances of water molecules in phase IV are found to be crystallographically nonequivalent. Conducting ion frequencies and the corresponding force constants have been determined for the analogous compounds MUP with M = K⁺, Na⁺, Ag⁺, NH⁺₄, Tl⁺ and H₃O⁺ and compared with other properties of these ionic conductors. Conductivity mechanisms in these materials are discussed.     

A study by E.S.R. of Mn2+ in potassium chromate

Divalent manganese ions are found in potassium chromate single crystals after heating at 600°C in the presence of iodine. These ions occupy three differently oriented sites with the same spin Hamiltonian parameters: g_z = 2·000, g_x = 2·008, g_y = 2·015; A_z = ?88·4 G, A_x = A_y = ?91 G; D = 190 and E = ?30 G.The authors suggest that Mn²⁺ occupies a substitutional (K⁺) position rather than an interstitial one. The influence of iodine is discussed.     

NMR Study of proton transport in crystalline antimonic acid

Pulsed ¹H NMR measurements are reported for polycrystalline antimonic acid (Sb₂O₅·nH₂O) in the temperature range 145 K<T<330 K at 60 MHz. Motional narrowing occurs at T>220 K and the relaxation behaviour is compatible with fast proton transport with a distribution of activation energies.