Contrasting effects of lanthanum and samarium modifiers on the elastic and non-linear acoustic properties of phosphate glasses

While samarium phosphate (Sm₂O₃) _x (P₂O₅)_(1?x) glasses are known to show pronounced long-wavelength acoustic-mode softening, their lanthanum (La₂O₃) _x (P₂O₅)_(1?x) analogues do not. To investigate experimentally this different influence of lanthanide modifiers, a comparative study has been made of the effects of temperature and pressure on the velocities of ultrasonic waves propagated in binary ((La₂O₃) _x (P₂O₅)_(1?x) and (Sm₂O₃) _x (P₂O₅)_(1?x)) and ternary ((La₂O₃) _x (Sm₂O₃) _y (P₂O₅)_(1?x?y)) phosphate glasses with compositions near to that corresponding to the metaphosphate (R₂O₃)_0.25(P₂O₅)_0.75. For each glass the second-order elastic stiffness tensor componentsC _IJ ^S continue to increase down to 10 K in a manner consistent with ultrasonic interactions with two-level systems. Measurements of the effects of hydrostatic pressure on the ultrasonic wave velocities have been used to determine the hydrostatic pressure derivatives (?C _IJ ^S /?P) _T,P=0 of the second-order elastic stiffness tensor components and (?B ₀ ^S /?P) _T,P=0 of the bulk modulusB ₀ ^S at room temperature (293 K). For the ternary glasses (?C ₁₁ ^S /?P) _T,P=0, (?C ₄₄ ^S /?P) _T,P=0 and (?B ₀ ^S /?P) _T,P=0 are small but positive; these glasses stiffen under pressure. Replacement of samarium by lanthanum in the ternary glasses negates the acoustic-mode softening. Possible sources of the different effects of lanthanum and samarium modifiers on the non-linear acoustic properties of metaphosphate glasses are discussed.     

Speciation of Zr(IV) radionuclides in solutions

The speciation of Zr(IV) radionuclides at their concentration of ～10^?13 M in the solution was studied. The pH ranges where Zr(IV) exists as ions or as pseudocolloids were determined. The Zr⁴⁺ hydrolysis yields Zr(OH)³⁺ and Zr(OH) ₂ ²⁺ complexes. Their stability constants were calculated. At [Zr(IV)] > 1 × 10^?5 M, binuclear hydroxo complexes Zr₂(OH) _z+ ^x are formed.     

Ba3(P1 − x Mn x O4)2 : Blue/green inorganic materials based on tetrahedral Mn(V)

We describe a blue/green inorganic material, Ba₃(P_1???x Mn _x O₄)₂ (I) based on tetrahedral MnO $_{4}^{3-}$ :3d ²chromophore. The solid solutions (I) which are sky-blue and turquoise-blue for x ≤ 0·25 and dark green for x ≥ 0·50, are readily synthesized in air from commonly available starting materials, stabilizing the MnO $_{4}^{3-}$ chromophore in an isostructural phosphate host. We suggest that the covalency/ionicity of P–O/Mn–O bonds in the solid solutions tunes the crystal field strength around Mn(V) such that a blue colour results for materials with small values of x. The material could serve as a nontoxic blue/green inorganic pigment.     

Oxygen ion conductivity of (Yb0.9 ? x Tb x Ca0.1)2Ti2O7 ? δ solid solutions

We have studied terbium substitution for ytterbium in (Yb_{0.9 ? x} Tb _x Ca_0.1)₂Ti₂O_{7 ? ??} (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550°C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb_0.9Ca_0.1)₂Ti₂O_6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: ??r = r(Tb _{CN 8} ³⁺ ) ? r(Yb _{CN 8} ³⁺ ) = 0.055 ?. The oxygen ion conductivity of the (Yb_{0.9 ? x} Tb _x Ca_0.1)₂Ti₂O_{7 ? ??} solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900°C. At high temperatures (t > 640°C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640°C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration.     

Electrical behaviour of doped-yttria stabilized zirconia ceramic materials

Single-phase sintered ceramic materials (ZrO₂)_1?x {(Y₂O₃) _y (RE₂O₃)_{1-y x} }_x (RE=Nd, Ce, Dy, Er), were synthesized and electrical conductivity and transport number measurements were made as a function of temperature between 500 and 1200° C. The activation energies of conduction were determined, and it was found that the charge carriers in these solid solutions are oxygen ions. The fabricated electrolyte discs were used in cells of the type \(P_{O_2 }\) , Pt/zirconia solid solution/ \(P_{\mathop O\limits^{'} _2 }\) , platinum where \(P_{O_2 }\) =air (0.21 atm) and \(P_{\mathop O\limits^{'} _2 }\) =1 atm or argon-O₂ mixtures. Below 700° C, the e.m.f. deviated from the theoretical values for completely ionic conduction; good agreement was observed above this temperature.     

Electrical and Thermal Transport Properties of Transition Metal Substituted in Electron-Doped La0.9Te0.1Mn1?x M x O3 Compounds (M=Cr and Al)

Systematical studies of resistivity ??(T), thermopower S(T), and thermal conduction ??(T) have been performed on the electron-doped manganites La_0.9Te_0.1Mn_1?x Cr(Al) _x O₃ (0.05??x??0.20). The Cr005 and Al005 samples exhibit an insulator-metal transition in the ??(T) curves, however, other samples present insulating behaviors in the whole measured temperature. The S(T) data increases with decreasing temperature and develop a peak at $T_{S}^{P}$ for all samples, with decreasing temperature further, another characteristic temperature $T_{s}^{m}$ is observed. The fits of ??(T) and S(T) data in the high temperature region are presented, and the result shows that the electron conduction is governed by the VRH mechanism for Al-doped samples and the SPC mechanism for Cr-doped ones. As to thermal conduction ??(T), it is suggested that it comes from two sides, one is the phonon-phonon scattering due to disorder and the other is the spin-phonon interaction.     

Mechanism of Np(VI) oxidation with ozone in alkaline solutions

Bubbling of an ozone-oxygen mixture containing 0.1?C0.5 vol % O₃ at a rate of 15?C20 l h^?1 through 13 ml of a 2 × 10^?5?1 × 10^?4 M solution of Np(VI) in 0.1 and 1 M LiOH leads to the formation of Np(VII). The initial rate increases approximately in proportion to [Np(VI)] and [O ₃ ^gas ]^0.5. Up to 80% of Np(VI) is oxidized at maximum. At the O₃ concentration in the gas phase increased to 1?C4 vol %, Np(VI) is oxidized completely. Under the same conditions, Np(VI) in a concentration of (1?C5) × 10^?3 M is oxidized to almost 100%. Analysis of published data and additional experiments on the reaction of O₃ with Np(VI) ions in LiOH solutions allow a conclusion that the ozonation involves the reactions O₃ + OH^? = HO ₂ ^? + O₂, O₃ + HO ₂ ^? + OH^? = O ₃ ^? + O ₂ ^? + H₂O, and O₃ + O ₂ ^? = O ₃ ^? + O₂, followed by O ₃ ^? + NpO₂(OH) ₄ ^2? = O₂ + NpO₄(OH) ₂ ^3? + H₂O. In addition, HO ₂ ^? reduces Np(VII) and Np(VI) and reacts with O ₃ ^? . Certain contribution is made by the reaction Np(VI) + O₃ = Np(VII) + O ₃ ^? . The dependence of the Np(VII) accumulation rate on [O ₃ ^gas ]^0.5 was interpreted in terms of the concept of a heterogeneous-catalytic process.     

Oxygen interstitial and vacancy conduction in symmetric Ln2 ± x Zr2 ± x O7 ± x/2 (Ln = Nd,Sm) solid solutions

We have compared (Ln_{2 ? x} Zr _x )Zr₂O_{7 + x/2} (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln₂(Zr_{2 ? x} Ln _x )O_{7 ? δ} (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd₂O₃-ZrO₂ (NdZrO) and Sm₂O₃-ZrO₂ (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm_{2 ? x} Zr _x )Zr₂O_{7 + x/2} (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H₂/Ar-He). The Ln_{2 ± x} Zr_{2 ± x} O_{7 ± x/2} (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) × 10^?3 S/cm at 750°C. The lower oxygen vacancy conductivity of the Ln₂(Zr_{2 ? x} Ln _x )O_{7 ? δ} (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln_{2 ? x} Zr _x )Zr₂O_{7 + x/2} (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln₂O₃ concentrations.     

Phosphors based on NaZr2(PO4)3-type calcium and strontium phosphates activated with Eu2+ and Sm3+

Ca_0.5Zr₂(PO₄)₃:Eu²⁺, Sr_0.5Zr₂(PO₄)₃:Eu²⁺, and Ca_0.5Zr₂(PO₄)₃:Eu²⁺, Sm³⁺ orthophosphates prepared through precipitation using sol-gel processes are analogs of NaZr₂(PO₄)₃ (NZP) and crystallize in space group R $\bar 3$ . Their crystallographic parameters determined by X-ray diffraction are consistent with the interatomic distances extracted from EXAFS data. Their luminescence spectra obtained under excitation in the range 300?C400 nm contain emission bands between 425 and 525 nm. Substitution of the larger sized cations Eu²⁺ and Sm³⁺ for Ca²⁺ shifts the emission bands to shorter wavelengths and reduces their width because of the decrease in the effect of the crystal field. Analysis of the spectra indicates that Eu²⁺ occupies two types of crystallographic sites (independent interstitial sites of different sizes and shapes in the NZP framework structure). Codoping with Eu and Sm has ensured luminescence with chromaticity coordinates approaching those of white light: (x = 0.27, y = 0.34).     

New Magnetic Phase Transitions in the Tetragonal Compounds PrBa2Cu3O6+x at Low Temperature

The anomalous magnetic properties of Pr ions in the PrBa₂Cu₃O_6+x system are investigated at low temperature. Measurements of the specific heat C _P(T) and the magnetic susceptibility χ(T) are performed on ceramic samples in the tetragonal structure with x=0.44 and x=0. Two new magnetic transitions are observed below the Néel temperature of the Pr antiferromagnetic ordering $T_{\mathrm{N}}^{\mathrm{Pr}} \sim 9\mbox{--}10~\mathrm{K}$ . The first one is observed at the low-critical temperature T _cr～4–5?K and the second one is observed at $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}} \sim 6\mbox{--}7~\mathrm{K}$ , respectively. Assuming that ΔC _P(T) can be used to represent the Pr contribution to the specific heat C _P(T), the data are well fitted for T<T _cr by using the development of ΔC _P(T)/T=ΔA(T ²)^?3/2 +Δγ+M(T ²) ¹ +m(T ²) ² . The values of the electronic coefficient Δγ are found much lower than all previous results obtained in compounds of the orthorhombic structure, and this is, in good agreement with the insulating character of our non-superconducting samples. The high values obtained for the coefficient M, permits us to confirm the existence of strong Pr–Pr exchange interactions. Some non-linear effects attributed to the values of the coefficient m are revealed and discussed in terms of the previous Pr–Cu coupling with a spin reorientation phase transition of both spin sublattices around $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}}$ . The appearance of a weak ferromagnetic tendency in the magnetic susceptibility analysis below T _cr, could be associated with the reordering of the Pr subsystem.     

Improved microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramic with Ba2+ substitution

The microwave dielectric properties of La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for wireless communications. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg_0.5?xBa_xSn_0.5)O₃ ceramics contained La₂Sn₂O₇. An apparent density of 6.54 g/cm³, a dielectric constant ( $ \varepsilon_{r} $ ε r ) of 20.1, a quality factor (Q  $ \times $ ×  f) of 51,600 GHz, and a temperature coefficient of resonant frequency ( $ \tau_{f} $ τ f ) of ?82 ppm/°C were obtained for La(Mg_0.43Ba_0.07Sn_0.5)O₃ ceramics that were sintered at 1,550 °C for 4 h.     

Effect of Zr substitution on microwave dielectric properties of Zn2SnO4 ceramics

The microwave dielectric properties of Zn₂(Sn_(1?x)Zr_x)O₄ ceramics were examined with a view to their exploitation for mobile communication. The Zn₂(Sn_(1?x)Zr_x)O₄ ceramics were prepared by the conventional solid-state method with various amount of Zr substitution. The diffraction peaks of Zn₂(Sn_(1?x)Zr_x)O₄ ceramics did not vary significantly as x varied. A density of 6.10 g/cm³ was obtained for Zn₂(Sn_0.99Zr_0.01)O₄ ceramic, sintered at 1,225 °C for 4 h. Dielectric constant (? _r ) of 9.6, quality factor (Q × f) of 87,000 GHz, and temperature coefficient of resonant frequency (τ _f ) of ?51 ppm/°C were obtained for Zn₂(Sn_0.99Zr_0.01)O₄ ceramics that were sintered at 1,225 °C for 4 h.     

Synthesis and crystal structure of a new Np(V) oxalate, Na4(NpO2)2(C2O4)3·6H2O

A new oxalate complex, Na₄(NpO₂)₂(C₂O₄)₃·6H₂O, with the Np:C₂O₄ ratio of 2:3 was synthesized and studied by single crystal X-ray diffraction. In the crystal, the NpO ₂ ⁺ cations and oxalate anions are bound in open networks [(NpO₂)₂(C₂O₄)₃] _n ^4n- parallel to the bc plane. The Na(1) cations are accommodated in large voids of the neptunyl oxalate networks with the formation of crimped mixed-cation layers of the composition [Na₂(NpO₂)₂(C₂O₄)₃] _n ^2n- . The negative charge of the layers is compensated by the Na(2) cations arranged between the layers. The Np atoms have a pentagonal bipyramidal coordination surrounding with the equatorial plane formed by the oxygen atoms of three oxalate anions. The structure contains tridentate-bridging and tetradentate-bridging oxalate anions.     

Effect of Te Substitution on (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7 (x=0.0 to 0.5) Superconductor

The (Tl_0.5Pb_0.5)Sr₂(Ca_1?x Te _x )Cu₂O_7??? (Tl-1212) superconductor for x=0.0 to 0.5 has been prepared and studied by a powder X-ray diffraction method, electrical resistance and AC susceptibility measurements. Most of the samples showed Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Te substitution (x??0.3) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature ( $T_{\mathrm{c\ onset}}$ ) between 92 and 97 K. Our results indicated the combined effects of Te substitution, heating temperature and heating time on the formation and optimization of the (Tl_0.5Pb_0.5)Sr₂(Ca_1?x Te _x )Cu₂O₇ superconductor.     

Crossover from Localized Spins to Weak Coupling Charge Carriers: Theory for Nuclear Spin-Lattice Relaxation in Copper Oxide HTSC

The dynamic spin susceptibility $\chi^{+,-}_{\mathrm{total}}(\omega,{\bf q})$ that takes into account the interplay of localized and itinerant charge carriers exhibits a diffusive-like, extremely narrow and sharp symmetric ring of maxima at very small wave vectors: $|{\bf q}|=q_{0}$ where q ₀∝ω/J≈10^?6 with the Nuclear Magnetic Resonance (NMR) frequency ω and the superexchange coupling constant J together with the peak at the antiferromagnetic wave vector Q=(π,π). The calculated plane copper ⁶³(1/T ₁) and oxygen ¹⁷(1/T ₁) nuclear spin-lattice relaxation rates from carrier-free right up to optimally doped La_2?x Sr _x CuO₄ are in good agreement with experimental data.     

Synthesis, Magnetic Properties, Magnetic Entropy and Arrot Plot of Antiferromagnetic Frustrated Er2Ti2O7 Compound

The pyrochlore $\mathrm{Er}_{2}^{3 +} \mathrm{Ti}_{2}^{4 +}\mathrm{O}_{7}^{2 -}$ was synthesized via a ceramic method using two different oxides (Er₂O₃ and TiO₂). The compound was found to crystallize in the cubic system with the $\mathrm{Fd}\overline{3}\mathrm{m}$ space group (No. 227). A magnetic study, carried out at 2 and 300 K under an applied magnetic field ?? ₀ H=0.05?T, has revealed a complex magnetic structure at low temperature. The effective paramagnetic moment $\mu_{\mathrm{eff}}^{\exp}$ , deduced from (????? ₀)^?1=f(T) curve, was found by assuming a zero moment on the transition metal atom Ti⁴⁺. The paramagnetic Curie?CWeiss temperature ?? _CW=?21.54?K, the nearest neighbor interaction J _nn =?2.30?K, the classical nearest neighbor J ^cl=?8.65?K and the dipolar D _nn =3.76?K interactions?? values have revealed an antiferromagnetic behavior for Er₂Ti₂O₇ compound at low temperature. We have also studied the effects of the magnetic field splitting of rare-earth atom Er³⁺ in the compound Er₂Ti₂O₇ curved Arrott plots.     

Synthesis and Characterization of MgB2 Thin Films Prepared by?2.4?Mhz Ultrasonic Spray Pyrolysis System

Nano-sized B and Mg powders have been successfully deposited onto single crystal MgO(100) and Al₂O₃(001) substrates using 2.4 MHz ultrasonic spray pyrolysis system and an appropriate solution to obtain thin films of MgB₂ superconductors. After an in-situ heating process, ??600?C1000 nm thick superconductor films were obtained. The microstructure, electrical, and magnetic properties were characterized by means of particle size analyzer, XRD, SEM?CEDX, R?CT, and M?CH analysis. The effect of particle concentration in the solution, spraying time, and heating temperature on the quality of the MgB₂ films were discussed. The best T _c and T _zero results were obtained to be 39.5 and 37.4 K, respectively, for the film deposited on the Al₂O₃(001) substrates. Magnetic properties of the MgB₂ films were investigated at 3 different temperatures and up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 4.0×10⁶ A?cm^?2 at 10 K for 0 T for the film deposited on the Al₂O₃(001) substrates. The results obtained were found to be highly dependant on the particle concentration in the solution, heating temperature of substrates and carrier gas flow rate during spraying.     

Relaxor behaviour and dielectric properties of BiFeO3 doped Ba(Zr0·1Ti0·9)O3 ceramics

Ba_1???x Bi _x (Ti_0·9Zr_0·1)_1???x Fe _x O₃ ( x = 0–0·075) ceramics are prepared using a conventional solid state reaction method. X-ray diffraction shows the presence of a single phase. Addition of Bi^3?+? and Fe^3?+? strongly influences the crystal structure and dielectric properties of the ceramics. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. Ba_0·99Bi_0·01(Ti_0·9Zr_0·1)_0·99Fe_0·01O₃ ceramic shows a relaxor behaviour at room temperature with Δ T _m =12 K. P– E hysteresis loop of the composition, x = 0·007, shows a remanent polarization ( P _r ) of 0·5 μC/cm² with a coercive field ( E _C ) of 2 kV/cm. Raman spectra of all compounds are performed and correlated well with the X-ray diffraction and dielectric measurement results.     

Heteroepitaxial growth of ZnO nanosheet bands on ZnCo2O4 submicron rods toward high-performance Li ion battery electrodes

We report the direct synthesis of ZnCo₂O₄ and ZnO/ZnCo₂O₄ submicron rod arrays grown on Ni foil current collectors via an ammonia-evaporation-induced method by controlling the ratio of Zn to Co. These three-dimensional (3D) hierarchical self-supported nanostructures are composed of one-dimensional (1D) ZnCo₂O₄ rods and two-dimensional (2D) ZnO nanosheet bands perpendicular to the axis of the each ZnCo₂O₄ rod. We carefully deal with the heteroepitaxial growth mechanisms of hexagonal ZnO nanosheets from a crystallographic point of view. Furthermore, we demonstrate the ability of these high-surface-area ZnO/ZnCo₂O₄ heterostructured rods to enable improved electrolyte permeability and Li ion transfer, thereby enhancing their Li storage capability (～900 mA·h·g^?1 at a rate of 45 mA·h·g^?1) for Li ion battery electrodes.      

An X-ray diffraction study of Rb[UO2(SeO4)F]·H2O

An X-ray diffraction study of Rb[UO₂(SeO₄)F]·H₂O (I) was performed. The compound crystallizes in the rhombic system with the following unit cell parameters: a = 8.4753(6), b = 13.5234(9), c = 13.5296(9) Å, space group Pnma, Z = 8, V = 1550.7(2) ų; R = 0.0248. The principal structural units of crystals of I are [UO₂(SeO₄)F]^? layers belonging to crystal-chemical group AT³M² (A = UO ₂ ²⁺ , T³ = SeO ₄ ^2? , M² = F^?) of uranyl complexes. The uranium-containing layered units are combined via electrostatic interaction with Rb cations and via a system of hydrogen bonds involving outer-sphere water molecules.