Superprotonic CsH<Subscript>2</Subscript>PO<Subscript>4</Subscript>-CsHSO<Subscript>4</Subscript> solid solutions

We have performed partial HSO₄⁻ substitution in CsH₂PO₄ and studied the associated structural changes and the proton conductivity of the resultant (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH₂PO₄ (sp. gr. P2₁/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH₂PO₄ (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH₂PO₄)_{1 − x} (CsHSO₄) _x solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching that of the superionic phase of CsH₂PO₄ in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH₂PO₄, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH₂PO₄ to 0.48 eV at x = 0.1.     

Thermoelectric power factor of Ti<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NiSn alloys

Ti_{1 − x} V _x NiSn (x = 0–0.10) substitutional solid solutions have been prepared by doping the intermetallic semiconductor n-TiNiSn (half-Heusler phase) with vanadium, a donor impurity, and their resistivity and thermopower have been measured at temperatures from 80 to 380 K. The results demonstrate that, when doping of TiNiSn causes no type inversion, the thermoelectric power factor of the solid solution markedly exceeds that of the undoped ternary compound.     

Composition and properties of compounds in the PbSe-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

To identify the compounds existing in the PbSe-Bi₂Se₃ system, Bridgman-grown ingots and annealed polycrystalline samples have been characterized by X-ray diffraction. The results indicate that the first solidified portion of the Bridgman-grown ingots consists of a PbSe-based solid solution with a cubic structure. Further directional solidification involves peritectic reactions that lead to the formation of the ternary compounds Pb₅Bi₆Se₁₄ and Pb₅Bi₁₂Se₂₃, which have monoclinic structures. The structural data have been used to refine the phase diagram of the PbSe-Bi₂Se₃ system. The thermoelectric properties of Pb₅Bi₆Se₁₄, Pb₅Bi₁₂Se₂₃, and Pb5Bi18Se32 have been studied using annealed polycrystalline samples. Their Hall coefficient and resistivity have been measured in the temperature range 80–670 K, and their thermoelectric power, electrical conductivity, and thermal conductivity have been measured from 80 to 370 K. The ternary compounds in the PbSe-Bi₂Se₃ system have low lattice thermal conductivity, which can be understood in terms of the key features of their crystal structure.     

A thermodynamic investigation of NdMe<Subscript>3</Subscript>Sr<Subscript>3</Subscript>Mn<Subscript>4</Subscript>O<Subscript>12</Subscript> (Me—Li,Na, K) manganites in the range from 298.15 to 673 K

High-temperature synthesis according to ceramic technology is used to prepare new manganites NdMe₃Sr₃Mn₄O₁₂ (Me—Li, Na, K). The X-ray powder method is used to find that the compounds crystallize in tetragonal syngony, and the parameters of their crystal lattices are determined. The method of dynamic calorimetry is used in the range from 298.15 to 673 K for determining the heat capacity of manganites; in so doing, the presence of second-order phase transitions is revealed. In view of phase transitions, equations are derived which describe the dependence C _p ^ℴ ∼ f(T) in the range from 298.15 to 673 K. The temperature dependences of permittivity and electrical resistance of manganites are investigated at 303–503 K; these dependences likewise confirm the presence of second-order phase transitions.     

Crossover Behavior of Variable Range Hopping in Bi-Doped C<Subscript>60</Subscript>

Abstract: Mott variable-range hopping (VRH) is characterized by an exp [1/T ^1/4] behavior in the temperature dependence of resistivity and is generally observed near the metal–insulator transition as electron screening increases and the Coulomb gap disappears near the metallic phase, while Efros–Shklovskii VRH, characterized by exp [1/T ^1/2], is found deeper in the insulating region. We have investigated the transport properties of Bi-doped fullerene C₆₀. Samples were prepared via solid state reaction in a sealed quartz tube near 600°C. The resistivity data can be fit with a single function exp [1/T ^υ ] (υ=1/4 or 1/2, depending on the Bi concentration) over the entire temperature range below 300 K and over 5–6 orders of magnitude in resistivity. υ changes from 1/4 to 1/2 as the Bi concentration increases, suggesting a crossover from Mott VRH to intergranular tunneling at higher Bi concentration. The thermoelectric Seebeck coefficient was also measured and is about 20 μV/K at room temperature. It decreases with decreasing temperature. The thermal conductivity of the doped samples is extremely low.     

Electrical conductivity studies of AgI–Ag<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–TeO<Subscript>2</Subscript> glasses

The silver ion conducting boro tellurite glasses have been prepared by melt quenching technique. The conductivity and dielectric measurements were carried out on these glasses as a function of frequency from 10 Hz to 10 MHz over a temperature range of 298–328 K. The analysis of conductivity measurement shows that the silver ions are the main charge carriers, which are considered to be the predominant factor playing the role of enhancing the conductivity. The power law exponent s and stretched exponent β are found to be insensitive to both temperature and compositions. AC conductivity and dielectric relaxation behaviour of these glasses were also studied and the results are discussed in view of the structure of borate and tellurite network.     

Thermodynamic simulation of phase equilibria in the UO<Subscript>2</Subscript>-Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> system at high temperatures

Thermodynamic models of a UO₂-based melt and cubic solid solution were developed on the basis of the most accurate measurements of the UO₂-Gd₂O₃ liquidus in a range of 0–30 mol. % of Gd₂O₃. These models enabled computing the phase diagram of this system in a temperature range of 1900–3200 K for all composition varieties.     

Thermoanalytical study of the polymorphism and melting behavior of Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

We have developed a procedure for the synthesis of phase-pure α- and β-Cu₂V₂O₇. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability range 25–610°C), while α-Cu₂V₂O₇ (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase γ-Cu₂V₂O₇, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu₂V₂O₇, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu₂V₂O₇, CuVO₃, and other compounds.     

Studies on a.c. properties of Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> perovskites

A.c. measurements were preformed on bulk samples of Ca_1−x Sr _x TiO₃ (CST) perovskites with x = 0, 0.1 and 0.5 as a function of temperature range 300–450 K and frequency range 10³–10⁵ Hz . The experimental results indicate that the a.c. conductivity σ_a.c.(ω), dielectric constant ε′ and dielectric loss ε′′ depend on the temperature and frequency. The a.c. conductivity as a function of frequency is well described by a power law Aω ^S with s the frequency exponent. The obtained values of s > 1 decrease with increasing temperature. The present results are compared to the principal theories that describe the universal dielectric response (UDR) behavior.     

Potassium ion conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>2</Subscript> solid electrolytes

New potassium ion conducting solid electrolytes based on potassium monoferrite have been prepared through partial substitution of the divalent cation Cd²⁺ on the potassium site, and their properties have been investigated. The introduction of cadmium cations sharply increases the electrical conductivity of KFeO₂ over the entire temperature range studied. In addition to the maximum in conductivity at the boundary of the K_{1 − 2x} Cd _x FeO₂ solid solution, there is a maximum at a higher cadmium content (x = 0.30–0.35). The possible origins of this maximum are discussed.     

Characterization of electrical behaviour of Si modified BaSnO<Subscript>3</Subscript> electroceramics using impedance analysis

The compounds BaSn_1−x Si _x O₃ (x = 0–15 mol%) have been prepared by high temperature solid-state reaction route. Powder X-ray diffraction pattern of the samples reveal the formation of a single phase solid solution. It was found that single phase compositions have a cubic crystal structure similar to that of pure barium stannate at room temperature. The a.c. impedance analysis has been carried out in the frequency range 100 Hz–1 MHz for temperature ranging from 300 K to 750 K. Analysis of a.c. impedance data using the complex impedance plane gives the a.c. and d.c. resistance of negative temperature resistance of coefficient (NTCR) electroceramics. Complex impedance plane and complex electric modulus formalism are employed to determine the inhomogeneous nature of the electroceramics. This reveals the presence of single elements in the equivalent circuit at elevated temperature. Grain effects are more prominent than that of grain boundary effect at elevated temperature in the material matrix. The electrical conductivity increases sharply with rise in temperature at elevated temperature due to the thermally activated cations. Master modulus analysis provided an evidence of non-exponential type conductivity relaxation occurring in the materials at higher temperatures.     

Electrical and optical properties of InSbSe<Subscript>3</Subscript> amorphous thin films

Electrical conductivity, I–V characteristics and optical properties are investigated for InSbSe₃ amorphous thin films of different thicknesses prepared by thermal evaporation at room temperature. The composition of both the synthesized material and thin films were checked by energy dispersive X-ray spectroscopy (EDX). X-ray analysis indicated that all samples under investigation have amorphous structure. The dc electrical conductivity was measured in the temperature range (303–393 K) and thickness range (149–691 nm). The activation energy ΔE _σ was found to be independent of film thickness in the investigated range. The obtained I–V characteristic curves for the investigated samples are typical for memory switches. The switching voltage increases linearly with film thickness in the range (113–750 nm), while it decreases exponentially with temperature in the range (303–393 K). The switching process can be explained according to an electrothermal process initiated by Joule-heating of the current channel. Measurements of transmittance and reflectance in the spectral range (400–2,500 nm) are used to calculate optical constants (refractive index n and absorption index k). Both n and k are practically independent of film thickness in the investigated range (149–691 nm). By analysis of the refractive index n the high frequency dielectric constant ε_∞ was determined via two procedures and was found to have the values of 9.3 and 9.15. Beyond the absorption edge, the absorption is due to allowed indirect transitions with energy gap of 1.46 eV independent on film thickness in the investigated range.     

Magnetic and Thermal Behavior of Ru<Subscript>0.9</Subscript>Sr<Subscript>2</Subscript>YCu<Subscript>2.1</Subscript>O<Subscript>7.9</Subscript> Magneto-Superconductor Synthesized by High-Pressure High-Temperature Technique

The structural, physical, and thermal property details of Ru_0.9Sr₂YCu_2.1O_7.9 (Y/Ru-1212) superconducting material synthesized through high pressure (6 GPa) and a high temperature (1400 °C) (HPHT) route are reported here. (Y/Ru-1212) crystallizes in P4/mmm tetragonal structure and is found free of any detectable impurities through X-ray diffractometry. Ru-spins are ordered magnetically above 145 K, with a sizeable ferromagnetic component at 5 K. Further clear diamagnetic transitions are seen in both zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibility measurements and exhibiting superconductivity below 50 K. Both the thermoelectric power (S) and thermal conductivity (κ) measurements show superconductivity onset below 50 K with S=0 at 30 K and a broad hump in heat capacity C _p (T) below 30 K. Heat capacity (C _p ) measurements also exhibit the magnetic ordering temperature as a hump below 145 K. The appearance of a hump in C _p (T), instead of a clear transition, is indicative of short range magnetic correlations like spin glass (SG). Neither the high (145 K) nor the low (30 K) temperature humps of C _p (T) could be analyzed quantitatively because of short magnetic correlations in former and mixing of both superconductivity and FM components in a later case. The observed data is compared with various reported Ru-1212 systems synthesized under normal pressure conditions. It is concluded that HPHT synthesized Y/Ru-1212 is a bulk superconductor below 30 K with a substantial FM component.     

Electrical conduction and relaxation mechanism in Li<Subscript>2</Subscript>AlZr[PO<Subscript>4</Subscript>]<Subscript>3</Subscript>

Li-ion electrolyte NASICON type Li₂AlZr[PO₄]₃ has been prepared by Solid State Reaction method. Formation of the sample has been confirmed by XRD and TGA–DTA analysis. Electrical conductivity studies have been performed in the frequency range 42 Hz–5 MHz within the temperature range 523–623 K using aluminium as blocking electrodes. The conductivity has been found to be 1 × 10⁻⁵ S cm⁻¹ at 623 K. Dielectric spectra show the decrease in dielectric constant with increase in frequency. Dielectric loss spectra reveal that dc conduction contribution predominates in the sample. Spectroscopic plots of complex modulus suggest the Non-Debye behaviour of the electrical relaxation within the temperature range studied.     

Characterization of spray deposited CoWO<Subscript>4</Subscript> thin films for photovoltaic electrochemical studies

Preparation of Cobalt tungstate (CoWO₄) thin film by spray pyrolysis with ammonical solution as a precursor is presented. The phase and surface morphology characterizations have been carried out by XRD and SEM analysis. The study of optical absorption spectrum in the wavelength range 350 – 850 nm shows direct as well as indirect optical transitions in the thin film material. The d. c. electrical conductivity measurements in the temperature range 310–500 K indicate semiconducting behavior of the thin film. The thin films deposited on fluorine doped tin oxide (FTO) coated conducting glass substrates were used as a photoanode in photovoltaic electrochemical (PVEC) cell with configuration: CoWO₄ | Ce⁴⁺, Ce³⁺ | Pt; 0.1 M in 0.1 N H₂SO₄. The PVEC characterization reveals the fill factor and power conversion efficiency to be 0.36 and 0.62%, respectively. The flat band potential is found to be −0.18 V (SCE).     

Impedance spectroscopy analysis of double perovskite Ho<Subscript>2</Subscript>NiTiO<Subscript>6</Subscript>

The electrical properties of double perovskite Ho₂NiTiO₆ (HNT) are investigated by impedance spectroscopy in the temperature range 30–420 °C and frequency range 100 Hz to 1 MHz. The X-ray diffraction analysis reveals that the compound crystallizes in monoclinic phase. The imaginary part of impedance (Z″) as a function of frequency shows Debye type relaxation. The frequency dependence of Z″ peak is found to obey an Arrhenius law with an activation energy of 0.129 eV. Impedance data presented in the Nyquist plot (Z″ vs. Z′) are used to identify an equivalent circuit and to know the bulk and interface contributions. The complex impedance analysis of HNT exhibits the appearance of both the grain and grain-boundary contribution. The results of bulk ac conductivity as a function of temperature and frequency are presented. The activation energy (0.129 eV), calculated from the slope of log τ versus 10³/T plot, is found to be the nearly same as calculated (0.130 eV) from dc conductivity. The frequency dependent conductivity spectra obey the power law.     

Preparation,crystal structure,and electrical conductivity of the solid electrolyte Zr<Subscript>0.86</Subscript>Sc<Subscript>0.12</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>1.93</Subscript>

The solid electrolyte Zr_0.88Sc_0.12Y_0.02O_1.93 for reduced-temperature SOFCs has been characterized by Rietveld X-ray powder diffraction analysis and conductivity measurements in the temperature range 295–970 K. Gas-tight nanostructured ceramic composites consisting of cubic, rhombohedral, and monoclinic phases have been produced by reaction sintering of mechanochemically prepared powders. The oxygen ion conductivity of the ceramic prepared by sintering at 1630 K, with a relative density of 94%, is three times lower than that of ceramics fabricated from DKKK Zr_0.89Sc_0.1Ce_0.01O_1.95 powder, but raising the sintering temperature to 1670 K increases the density of the ceramic to 99%, and its conductivity reaches the level of the DKKK ceramics. The core-shell ceramic nanocomposite obtained in this study possesses high mechanical strength and a reduced activation energy for grain-boundary conduction.     

Martensitic phase transformation in single crystal Co<Subscript>5</Subscript>Ni<Subscript>2</Subscript>Ga<Subscript>3</Subscript>

The magnetic, thermal, and transport properties of martensitic phase transformation in single crystal Co₅Ni₂Ga₃ have been investigated. The single crystal Co₅Ni₂Ga₃ shows martensitic transformation at 251 K on cooling and 254 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve, and temperature-dependent thermal conductivity curve are observed at martensitic transformation temperature (T _M). Negative magnetoresistance due to spin disorder scattering was observed in Co₅Ni₂Ga₃ single crystal at all temperature range. The temperature-dependent negative magnetoresistance shows a peak at T _M, which indicates that the spin disorder increases in the process of phase transition. Co₅Ni₂Ga₃ sample exhibits a temperature dependence of thermal conductivity κ(T) (dκ/dT > 0) due to electrons being above temperature 100 K.     

Structural and electrical properties of Ba<Subscript>5</Subscript>SmTi<Subscript>3</Subscript>V<Subscript>7</Subscript>O<Subscript>30</Subscript> ceramics

Polycrystalline sample of Ba₅SmTi₃V₇O₃₀ was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray preliminary structural studies reveal that the material has orthorhombic structure at room temperature. Detailed electrical (dielectric and impedance) properties of the material studied by using a complex impedance spectroscopy (CIS) technique in a wide temperature range (33–450 °C) at different frequencies (10²–10⁶ Hz) reveal that the relative dielectric constant of the material increases with rise in temperature and thus bulk has a major contribution to its dielectric and electrical properties. The bulk resistance of the material decreases with rise in temperature exhibiting a typical negative temperature coefficient of resistance (NTCR) behavior. The nature of the temperature variation of conductivity and value of activation energy, suggest that the conduction process is of mixed-type (ionic–polaronic and space charge). The existence of ferroelectricity in the compound was confirmed from polarization study.     

Bulk ac conductivity studies of lithium substituted layered sodium trititanates (Na<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript>)

Lithium mixed sodium trititanates with 0.3, 0.5 and 1.0 M percentage of Li₂CO₃ (general formula Na_2−X Li _X Ti₃O₇) have prepared by a high temperature solid-state reaction route. EPR analysis, high temperature range (473–773 K) and variable frequency range (100 Hz–1 MHz) ac conductivity measurements were carried out on prepared sample. The lithium ions are accommodated with the sodium ions in the interlayer space. The EPR specta of lithium mixed sodium Trititanates confirm the partial reduction of Ti⁴⁺ ions to Ti³⁺. Four distinct regions have identified in the LnσT versus 1,000/T plots. Various conduction mechanisms which dependence on concentration, frequency and temperature are reported in this paper for lithium mixed layered sodium Trititanates. The dilation of interlayer space has further been proposed to occur due to inclusion of lithium ions in the interlayer space. The conductivity increases as the concentration of lithium increases. The increase of ionic conductivity in these compounds is due to accommodation of lithium ions with sodium ions in interlayer space.