Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

Studies on ionic transport properties of a new Ag+ ion conducting composite electrolyte system (1−x)[0·75 AgI: 0·25 AgCl]:xSnO2

A new Ag⁺ ion conducting composite electrolyte system (1−x)[0·75 AgI: 0·25 AgCl]:xSnO₂ using a quenched/annealed [0·75 AgI: 0·25 AgCl] as host compound in place of conventional host AgI, has been investigated. The effects of various preparation methods and soaking time are reported. The composition 0·8[0·75 Agl: 0·25 AgCl]:0·2SnO₂ exhibited optimum conductivity (σ = 8·4 × 10⁻⁴S/cm) with conductivity enhancement of ∼ 10¹ from the annealed host at room temperature. Transport property studies such as electrical conductivity (σ) as a function of temperature using impedance spectroscopy technique, ionic transference number (t _ion) using Wagner’s d.c. polarization method and ionic mobility (μ) by transient ionic current technique were carried out on the optimum conducting composition. The mobile ion concentration (n) was calculated from ‘σ’ and ‘μ’ data.     

Thermoelectric power in Gd3+-substituted Cu-Cd ferrites

Polycrystalline Cd _x Cu_1−x Fe_2−y Gd _y O₄ ferrites fory=0·0 and 0·1 were prepared by ceramic technique. X-ray diffractograms of powder samples show cubic symmetry withx⩾0·2 fory=0·0 and 0·1, while compositions withx=0·0 fory = 0·0 and 0·1 are tetragonal. The thermopower measurements for Gd³⁺-undoped ferrites in the temperature range 300 K to 788 K shown-type conductivity forx⩾0·2. The substitution of Gd³⁺ changedn-type conductivity of the compositions top-type. The mobilities calculated show decreasing trend on Gd³⁺ substitution. The values of activation energy ΔE and drift mobilityE _d suggest polaron formation in substituted samples. The conduction mechanism is explained on the basis of localized model and formation of Gd³⁺+Fe²⁺ stable pairs at B site and Cu¹⁺+Fe³⁺ at A site.     

An analysis of the electrical conductivity of the Ag2SO4-K2SO4 binary system

Electrical conductivity of the Ag₂SO₄-K₂SO₄ binary system shows three maxima at 20, 70 and 90 mole% of K₂SO₄ added to Ag₂SO₄. The first and the third maxima have been explained in the light of intragrain percolation due to lattice distortion, whereas, the second maximum by the surface percolation. The limit of solid solubility has been set at 20 mole% on the basis of evidences obtained from XRD, DTA and SEM techniques.     

Effect of praseodymium substitution on the growth and properties of Y1−x Pr x Ba2Cu3O7−δ (o <x < 0·4) single crystals

In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium substituted (partially) large single crystals of high temperature superconducting Y_1−x Pr _x Ba₂Cu₃O_7−δ (x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm³ and 4 × 1 × 1 mm³, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y_0·8Pr_0·2Ba₂Cu₃O_7−δ and Y_0·6Pr_0·4Ba₂Cu₃O_7−δ materials are ≈ 2 × 3 × 0·1 mm³ and 5 × 1 × 1 mm³ and ≈ 1 × 1·5 × 0·1 mm³ and 7 × 0·2 × 0·1 mm³, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T _c) of the oxygenated crystals were found to depend on the Pr-content. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Water vapor absorption and proton conductivity of (Ba1−x La x )2In2O5+x

The proton conductivity of (Ba_1−x La _x )₂In₂O_5+x system has been investigated as a function of the La content, temperature and amount of absorbed water. The proton conductivity increased with La content up to x = 0.10, to reach a maximum of 1.12 × 10⁻⁵ (S/cm) at 400 °C. From that point on, it decreased. From the results of thermogravimetry and mass spectra, we confirmed that the water was absorbed in the (Ba_1−x La _x )₂In₂O_5+x system, in a maximum quantity of 0.14 mol/mol (sample). The proton conductivity increased monotonically with the quantity of water uptake, suggesting that this variable is one of the dominant parameter of proton conductivity in this system.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

Synthesis and characterization of nano-sized BaxSr1?xSO4 (0 ≤ x ≤ 1) solid solution by a simple surfactant-free aqueous solution route

A facile aqueous solution route has been employed to synthesize Ba _x Sr_1−x SO₄ (0 ≤ x ≤ 1) solid solution nanocrystals at room temperature without using any surfactants or templates. The as-synthesized products were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), scanning electron microscopy (SEM), and differential scanning calorimetry-thermogravimetry (DSC-TG). The Ba _x Sr_1−x SO₄ solid solution nanocrystals exhibit an orthorhombic structure and an ellipsoidal-shaped morphology with an average size of 80–100 nm. The lattice parameters of Ba _x Sr_1−x SO₄ solid solution crystals increase with increasing x value. However, they are not strictly coincident with the Vegard’s law, which indicates that the as-obtained products are non-ideal solid solutions. The Ba _x Sr_1−x SO₄ solid solution nanocrystals have an excellent thermal stability from ambient temperature to 1300°C with a structural transition from orthorhombic to cubic phase at about 1111°C.     

Magnetization and initial permeability studies of Nd3+ substituted Zn-Mg ferrite system

Polycrystalline ferrites, Zn _x Mg_1−x Fe_2−y Nd _y O₄ (x=0·00, 0·20, 0·40, 0·60, 0·80 and 1·00;y=0·00, 0·05 and 0·10), were prepared by standard ceramic method. The compositions, on characterization by X-ray diffraction, showed formation of single phase cubic spinels. Magnetic study of the compositions showed increase in magnetic moment,nβ, with Zn²⁺ concentration up tox=0·4 and a decrease thereafter. This was attributed to the existence of canted spin. The compositions forx=0·8 and 1·0 showed paramagnetic behaviour at and above room temperature. The substitution of Nd³⁺ ion caused reduction in the magnetic moment and Curie temperatures. Substituted Nd³⁺ ion showed its occupancy on octahedral (B) site. The dependence of the initial permeability was studied in the temperature range 298 K-700 K. This μ_i-T curve reflects the positive temperature coefficient of initial permeability for the compositionsx≤0·4 andy=0·00. On substitution of Nd³⁺ ion (i.e.y=0·05 and 0·10), the μ_i-T curves flatten, showing almost temperature independence of initial permeability. This is explained by positive contribution to the anisotropy constant,K ₁, by substituted rare-earth, Nd³⁺ ion.     

Conduction mechanism in Sn4+ substituted copper ferrite

Thermoelectric power (α) and electrical resistivity (ρ) are reported for the system Cu_1+x Sn _x Fe_2−2x O₄ (wherex=0·05, 0·1, 0·15, 0·2 and 0·3) from room temperature to 800 K. The compositions withx=0·05 and 0·2 exhibitn-type conduction while the compositions withx=0·1 and 0·15 showp- ton-type conduction change after 423 K. The conduction at low temperature (i.e. < 400 K) is due to impurities, while at higher temperature (i.e. > 400 K), it is due to polaron. Hopping conduction phenomenon for the present system has been explained on the basis of localized model of electrons. Additional localization may arise due to Sn⁴⁺ + Fe²⁺ stable pairs at B-site and Cu¹⁺ + Fe³⁺ pair at A-site.     

Effect of calcium substitution on superconductivity and hole concentration in La1·5Ba1·5Cu3O z

The superconducting properties of single phase La_1·5−x Ca _x+y Ba_1·5−y Cu₃O _z , 0·0≤x≤0·60 (LC) and 0·0≤y≤0·70 (CB), compounds with tetragonal triple-perovskite structure are studied, using X-ray diffraction for their resistivity, a.c. susceptibility, and oxygen-content. La_1·5−x Ca _x Ba_1·5Cu₃O _z (LC) samples, 0·15≤x≤0·60, are superconducting withT _c ^R=0 between 40 and 74 K. With the increase inx, the oxygen content, hole concentration in the CuO₂ layers as well as theT _c increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LaCa_0·5+y Ba_1·5−y Cu₃O _z (CB) compounds increase with the increase iny, theT _c ^R=0 remains nearly constant around 74 K fory=0·0−0·70. A correlation exists between theT _c and the hole concentration for LC and CB compounds.     

Structural,Magnetic, Optical and Electrical Properties of Ba Substituted BiFeO3

Ba²⁺ substituted bismuth ferrite (BFO) (Bi_1?x Ba _x FeO₃, x=0, 0.1, 0.2, and 0.3) was prepared by chemical route using nitrates as a precursor, and sintered at 830 °C for 1 hr. The structural, optical, magnetic, and electrical properties of the prepared samples were investigated to understand the effect of Ba²⁺ substitution in BFO. The samples were characterized by X-ray diffraction (XRD), and shows an impurity phase which reduces drastically on substitution. Magnetic measurements were carried out at room temperature up to a field of 20 kOe. Magnetic hysteresis loops revealed a significant change in magnetization on Ba²⁺ substitution in BFO with unsaturated nature. Further, the Fourier transformed Infrared (FTIR) and Ultra Violet Visible (U-V Vis) spectra of the samples at room temperature shows as a change in spectral behavior on substitution. The AC electrical conductivity analyzed through Impedance analyser at different temperatures and frequencies. The ac conductivity and its activation energies for the samples are found to be frequency and temperature dependent and also vary with Ba²⁺ substitution in BFO.     

Synthesis of hexagonal Al2−x Cr x O3 nanodisks by a thermal decomposition of mesoporous Cr4+:Al2O3 powders

Monodispersed hexagonal Al_2−x Cr _x O₃ nanodisks are synthesized through a reactive doping of Cr⁶⁺ cations in a hydrogenated mesoporous AlO(OH)·αH₂O powder followed by annealing at 1,200 °C in air. The reaction was carried out by a drop wise addition of an aqueous Cr⁶⁺ solution (0.5–1.0 M) to AlO(OH)·αH₂O, at room temperature. Al_2−x Cr _x O₃ nanostructure formation was controlled by the nucleation and growth from the intermediate amorphous mesoporous Cr⁴⁺:Al₂O₃ composites in the temperature range 400–1,000 °C. The nanodisks of ∼50 nm diameter and thickness of ∼16 nm is observed in the sample with x of 0.2 and similar nanodisks with a low dimension is observed at a higher value of x of 1.6 (after 2 h of heating at 1,200 °C). The Cr³⁺ ↔ Al³⁺ substitution, x ≤ 1.2, inhibits grain growth in small crystallites. The crystallites in x = 0.2 composition have 43 nm diameter while it is 15 nm in those with x = 1.2 composition.     

Structural and electrical properties of the system ZnFeMnO4 - GaCoMnO4

X-ray crystallographic and electrical conductivity studies of the system ZnFeMnO₄ - GaCoMnO₄ were carried out with a view to investigating the cation distribution. The system is tetragonal in the range of 0⩽x⩽20 and cubic in the range 40⩽x⩽100 (wherex denotes the mole percentage of GaCoMnO₄). The plot ofV ^1/3 vs composition shows a break at the transition region. The value of oxygen ion parameter (u) decreases with increase in concentration of a⁸G⁺ atA-site. The electrical resistivity-temperature behaviour obeys Wilson’s law. Thermoelectric coefficient (α) values vary between 37 and 230μV/K. The mobility of holes calculated from IR and conductivity data is of the order of 10⁻⁹cm²/V-sec. X-ray intensity calculations and conductivity measurements suggest the ionic configuration of the system to be, Zn _1−x ²⁺ Ga _x ³⁺ [Fe _1−x ³⁺ Co _x ²⁺ Mn³⁺]O ₄ ²⁻     

Rubidium ion conducting Rb2 ? 2xAl2 ? xAxO4 (A = Nb, Ta) solid electrolytes

Rb_{2 − 2x} Al_{2 − x} A _x O₄ (A = Nb, Ta) solid solutions have been synthesized, and their conductivity has been measured as a function of temperature and composition. The highest rubidium ion conductivity in the Rb_{2 − 2x} Al_{2 − x} A _x O₄ solid solutions is 3.16 × 10⁻³ S/cm at 300°C and ∼ 2 × 10⁻² S/cm at 700°C. The high rubidium ion conductivity of the synthesized solid electrolytes is mainly due to the formation of rubidium vacancies when Nb⁵⁺ or Ta⁵⁺ substitutes for Al³⁺ and to the specific features of the crystal structure of RbAlO₂.     

Superconductivity in compound Y1-2x Ce x Ba2+x Cu3O6·5+δ system

Partial substitution of Ce in place of Y has been achieved by taking care of charge compensation and compounds with the general formula Y_1-2 xCe_xBa₂₊ xCu₃O_6·5+δ have been successfully prepared. X-ray powder diffraction analysis reveals that this substitution gives orthorhombic single phase for 0⩽x⩽0·3. TheT _c remains nearly unchanged between 94-90 K.     

Protonic conduction in Al2(SO4)3·16H2O: coulometry,transient ionic current,infrared and electrical conductivity studies

Proton transport in Al₂(SO₄)₃·16H₂O has been established using different techniques namely coulometry, transient ionic current, i.r., DTA/TGA and electrical conductivity. The possible charge carriers are H⁺ and OH⁻ generated as a result of possible electrolysis of hydrate water molecules. The mobilities of the two charge carriers are approximately 4×10⁻⁵ and 2.4×10⁻⁵cm²V⁻¹s⁻¹. The electrical conductivity shows strong dependence upon humidity and also shows a against 1/T behaviour closely related with its thermal dehydration reaction.     

Lithium borosulphate glasses: an analysis of glass transition temperature results

Lithium borosulphate glasses have been prepared in three different series: (a) (42·5 −x)Li₂O:57·5 B₂O₃:xLi₂SO₄; (b) 42·5Li₂O: (57·5 −x)B₂O₃:xLi₂SO₄ and (c) 42·5Li₂O:57·5B₂O₃:xLi₂SO₄. The glass transition temperature (T _g) of these glasses has been analysed on the basis of the fraction of four coordinated boron which governs the glass structure. The analysis reveals that the addition of Li₂SO₄ in series (a) and (b) gives rise to increased value of N₄ whereas, in series (c) it increases the number of non-bridging oxygens.     

Superconductivity of Hg(1−x)AgxBa1.9La0.1CuOy (0≤x≤0.6) Materials

Hg_(1?x)Ag_xBa_1.9La_0.1CuO_y materials are prepared directly from the oxide powders. Substitution of 5 at.% La³⁺ for Ba²⁺ chemically stabilize the materials. Ag substitution for Hg increases the Superconducting volume and enhances the Superconducting grain size. The Lattice parameters of the Superconducting tetragonal phase do not change but T_c decreases with increasing Ag-concentration from 92.5 (x = 0) to 78 K (x = 0.6). Maximum intra-grain critical current density estimated from the magnetization data is 1.4 × 10⁶ A/cm² (70 K, H = 0) for the composition Hg_0.8Ag_0.2Ba_1.9La_0.1CuO_y. Ag substitution for Hg transforms the semiconducting HgBa_1.9La_0.1CuO_y to metallic state and the electrical resistivity of the materials decreases with increasing Ag-concentration. Inter-grain critical current density increases with Ag-concentration and a maximum value of 25A/cm² (77 K; H = 0) is observed. This indicates that the presence of Ag provides extra pinning centers in the grains or at the grain boundaries and enhances the inter-grain electrical conductivity.     

Superstructures in Ba0·6K0·4BiO3−y and BaPb1−x Bi x O3−y

The perovskite compounds Ba_0·6K_0·4BiO₃ and BaPb_1−x Bi _x O₃ (x=0·9, 0·5, 0·25) have been investigated by high resolution electron microscopy and selected area electron diffraction. Several superlattices produced byin situ electron beam reduction have been observed. Ordered atomic arrangements in the reduced materials are discussed.