Dielectric, elastic, anelastic and conductivity behaviour of ferroelectromagnetic composites, Ni0·5Zn0·5Fe1·95O4?δ + Ba0·8Pb0·2TiO3

Ferroelectromagnetic composites with compositions, X Ni_0·5Zn_0·5Fe_1·95O_4−δ + (1 − X) Ba_0·8Pb_0·2TiO₃, in which X varies as 0, 0·005, 0·010, 0·015, 0·020, 0·040, 0·060, 0·080 and 1 in mole %, were prepared by conventional ceramic double sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric constant, ɛ′, dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in the temperature range 30–350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data were discussed in the light of phase transitions.     

Thermal Conductivity of a Simulated Fuel with Dissolved Fission Products

The thermal diffusivity of a simulated fuel with fission products forming a solid solution was measured using the laser-flash method in the temperature range from room temperature to 1673 K. The density and the grain size of the simulated fuel with the solid solutions used in the measurement were 10.49 g · cm⁻³ (96.9% of theoretical density) at room temperature and 9.5 μm, respectively. The diameter and thickness of the specimens were 10 and 1 mm, respectively. The thermal diffusivity decreased from 2.108 m² · s⁻¹ at room temperature to 0.626 m² · s⁻¹ at 1673 K. The thermal conductivity was calculated by combining the thermal diffusivity with the specific heat and density. The thermal conductivity of the simulated fuel with the dissolved fission products decreased from 4.973 W · m⁻¹ · K⁻¹ at 300 K to 2.02 W · m⁻¹ · K⁻¹ at 1673 K. The thermal conductivity of the simulated fuel was lower than that of UO₂ by 34.36% at 300 K and by 15.05% at 1673 K. The difference in the thermal conductivity between the simulated fuel and UO₂ was large at room temperature, and decreased with an increase in temperature. Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

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.     

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.     

Preparation and properties of (CdS) x -(PbS)1 −x thin-film composites

A modified chemical deposition process is employed for the preparation of thin-film (CdS) _x -(PbS)_{1 −x} composites with 0·2 ≤x ≤ 0·8. Cadmium sulphate, lead acetate and thiourea are used as the basic source materials. The electrical conductivity is found to decrease with increasing composition parameterx up to 0·5 and increase for further increase inx. The composites are polycrystalline as is revealed from XRD and microscopic observations and show phases of both cubic and hexagonal CdS, cubic CdO and PbS, and tetragonal PbO and PbO₂. Additional peaks of free elemental Cd and S have also been observed. For all the phases no significant variation in lattice parameters withx has been observed. The optical absorption studies show the presence of four well-defined absorption edges at approximately 0·45 eV, 1·05eV, 1·80 eV and 2·35 eV, at the same energies for allx values. The absorption coefficient is of the order of 10⁴ cm⁻¹ and mode of band-to-band transition is of the direct type.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

n-CuInS2/polysulfide photoelectrochemical solar cells prepared by spray pyrolysis

n-CuInS₂ photoanode has been prepared by spray pyrolysis onto SnO₂ deposited glass substrate at 350°C. The conductivity type of the photoanode was tested by hot-probe method and was ofn type. The conductivity of the photoanode was of the order of 2–4Θ⁻¹cm⁻¹ and was measured by using four-probe method. The effect of etching (HCl:HNO₃ = 5:1 by volume) on photoanode properties has been studied. The best cell had the following parameters:V _oc = 0·29V,I _sc = 5·33 mA/cm²,ff = 0·571 and η = 1·275%.     

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.     

Effect of oxygen intercalation on properties of sputtered CuYO<Subscript>2</Subscript> for potential use as <Emphasis Type="Italic">p</Emphasis>-type transparent conducting films

Transparent films of copper yttrium oxide doped with 2% calcium have been prepared by rf magnetron sputtering. The films show a conductivity of 8 Scm⁻¹ on intercalation of oxygen at high pressure, which reduced the transparency in the visible region. The Ca-doped CuYO₂ films before oxygen intercalation show an average transmission of about 60% which reduces to about 45% upon oxygen intercalation. The temperature dependence of the conductivity indicates semiconductor behaviour with low activation energy of 0·59 eV at room temperature. The positive sign of Seebeck coefficient (+274 μVK⁻¹) confirms the p-type conductivity of the films. The optical bandgap of CuYO₂ was found to be 3·15 eV.     

EPMA,EPR, electronic and vibrational spectral studies on natural aurichalcite

The electron probe micro analysis (EPMA), electron paramagnetic resonance (EPR), electronic and vibrational spectral studies on a natural mineral, aurichalcite were studied at room temperature. The EPMA analysis revealed the concentration of copper in the mineral to be 2·6 wt% and zinc as 24·5 wt%. The optical spectra revealed the presence of copper inD _4h symmetry with crystal field (Dq) and tetragonal field (Ds andDt) parameters as 1250, 1600 and 520 cm⁻¹ respectively. This further confirmed the presence of Cu(II) ion in an elongated tetragonal site. The EPR studies indicated the presence of Cu(II) ion, but hyperfine lines could not be resolved due to the high concentration of the paramagnetic impurity in the mineral. The IR spectrum confirmed the presence of water and carbonate ion.     

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.     

Effect of sintering temperature on structural and electrical properties of gadolinium doped ceria (Ce<Subscript>0·9</Subscript>Gd<Subscript>0·1</Subscript>O<Subscript>1·95</Subscript>)

Gadolinium doped ceria oxide is one of the promising materials as an electrolyte for IT-SOFCs. Ce_0·9Gd_0·1O_1·95 (GDC10) powder was prepared by solid state reaction and sintered at 1473 K, 1573 K, 1673 K and 1773 K. All samples were studied using X-ray diffraction, scanning electron micrograph and d.c. conductivity measurement. The crystallinity and surface morphology of the samples improved with sintering temperature. Further, the electrical conductivity measurement indicated that the conduction mechanism is mainly ionic. The conductivity of samples sintered at 1673 K and 1773 K at 800°C are of the order of 0·1 S-cm⁻¹. The activation energies decreased from 1·25–0·82 eV with increase in sintering temperature.     

Thermal Diffusivity and Heat of Formation of Harzburgite and Its Major Constituent Minerals

The thermal diffusivity, D, and its temperature dependence of Oman harzburgite rock and its major mineral olivine have been evaluated from the basic properties such as seismic velocities, density, and Debye temperature. The Arrhenius-type temperature dependence of the diffusivity was utilized to evaluate the heat of formation, ΔH _D. The diffusivity values, 1.80mm² · s⁻¹ and 2.1mm² · s⁻¹ obtained at room temperature for harzburgite and olivine, respectively, are consistent with available data. The diffusivity values for Oman harzburgite are overestimated by an amount of 0.27mm² · s⁻¹ relative to those of PNG harzburgite. The ΔH _D value (−2.40 kJ · mol⁻¹) for harzburgite rock of the Oman ophiolite suite is comparable with that (−2.90 kJ · mol⁻¹) of the harzburgite rock of Papua New Guinea. The disagreements in the thermal diffusivity and heat of formation values may be partly due to ignoring the effect of pyroxene in Oman harzburgite.     

Effect of annealing on d.c. conductivity of V2O5-SnO-TeO2 glasses

The d.c. conductivity (σ) of V₂O₅-SnO-TeO₂ glasses prepared by the press-quenching method was studied at temperatures from room temperature (RT) to 473 K, and the effect of annealing on σ was investigated. The conductivity of 50V₂O₅·20SnO·30TeO₂ glass was determined to be 3.98×10⁻⁴ Scm⁻¹ at 473 K and was unchanged for annealing (6–48 h) at 493 K, lower than T_g = 501 K, while its density increased with annealing time. These glasses were found to be n-type semiconductors, and the conduction was confirmed to be due to adiabatic small polaron hopping for V₂O₅ ≧ 50 mol%, and non-adiabatic for V₂O₅ < 50 mol%. The activation energy for conduction, W, decreased with annealing time. Variations in oxygen molar volume of the glasses with annealing time inferred a change in glass structure, from loosely to closely packed, resulting in a decrease in vanadium ion spacing with annealing. This caused an increase in the polaron band width, producing a decrease in polaron hopping energy and W. The effect of annealing time on the density of 50V₂O₅·20SnO·30TeO₂ glass was explained adequately by Winter's formula.     

A Study of Specific Heat Capacity Functions of Polyvinyl Alcohol–<Emphasis Type="Italic">Cassava</Emphasis> Starch Blends

The specific heat capacity (C _sp) of polyvinyl alcohol (PVOH) blends with cassava starch (CSS) was studied by the differential scanning calorimetry method. Specimens of PVOH–CSS blends: PPV37 (70 mass% CSS) and PPV46 (60 mass% CSS) were prepared by a melt blending method with glycerol added as a plasticizer. The results showed that the specific heat capacity of PPV37 and PPV46 at temperatures from 330 K to 530 K increased from (2.963 to 14.995)  J· g⁻¹ · K⁻¹ and (2.517 to 14.727)  J · g⁻¹· K⁻¹, respectively. The specific heat capacity of PVOH–CSS depends on the amount of starch. The specific heat capacity of the specimens can be approximated by polynomial equations with a curve fitting regression > 0.992. For instance, the specific heat capacity (in J · g⁻¹ · K⁻¹) of PPV37 can be expressed by C _sp = −17.824 + 0.063T and PPV46 by C _sp = −18.047 + 0.061T, where T is the temperature (in K).     

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     

Vacuum Insulation Panels – Exciting Thermal Properties and Most Challenging Applications

Vacuum insulation panels (VIPs) have a thermal resistance that is about a factor of 10 higher than that of equally thick conventional polystyrene boards. VIPs nowadays mostly consist of a load-bearing kernel of fumed silica. The kernel is evacuated to below 1 mbar and sealed in a high- barrier laminate, which consists of several layers of Al-coated polyethylene (PE) or polyethylene terephthalate (PET). The laminate is optimized for extremely low leakage rates for air and moisture and thus for a long service life, which is required especially for building applications. The evacuated kernel has a thermal conductivity of about 4 × 10⁻³ W · m⁻¹ · K⁻¹ at room temperature, which results mainly from solid thermal conduction along the tenuous silica backbone. A U-value of 0.2 W · m⁻² · K⁻¹ results from a thickness of 2 cm. Thus slim, yet highly insulating fa?ade constructions can be realized. As the kernel has nano-size pores, the gaseous thermal conductivity becomes noticeable only for pressures above 10 mbar. Only above 100 mbar the thermal conductivity doubles to about 8 × 10⁻³ W · m⁻¹ · K⁻¹, such a pressure could occur after several decades of usage in a middle European climate. These investigations revealed that the pressure increase is due to water vapor permeating the laminate itself, and to N₂ and O₂, which tend to penetrate the VIP via the sealed edges. An extremely important innovation is the integration of a thermo-sensor into the VIP to nondestructively measure the thermal performance in situ. A successful “self-trial” was the integration of about 100 hand-made VIPs into the new ZAE-building in Würzburg. Afterwards, several other buildings were super-insulated using VIPs within a large joint R&D project initiated and coordinated by ZAE Bayern and funded by the Bavarian Ministry of Economics in Munich. These VIPs were manufactured commercially and integrated into floorings, the gable fa?ade of an old building under protection, the roof and the facades of a terraced house as well as into an ultra-low-energy “passive house” and the slim balustrade of a hospital. The thermal reliability of these constructions was monitored using an infrared camera.Invited paper presented at the Seventh European Conference on Thermophysical Properties, September 5-8, 2005, Bratislava, Slovak Republic.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

An analysis of the electrical conductivity in BaSO4-added Ag2SO4 solid electrolyte system

The compositions (1 −x)Ag₂SO₄−(x)BaSO₄, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba²⁺ in Ag₂SO₄ was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained using a detailed impedance analysis. The partial substitution of Ba²⁺ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model based on lattice distortion (expansion) due to partial substitution of Ag⁺ by the bigger Ba²⁺ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO₄-dispersed Ag₂SO₄ conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO₄ dispersed Ag₂SO₄ is due to percolation threshold.     

Application of photoacoustic and photothermal techniques for heat conduction measurements in a free-standing chemical vapor-deposited diamond film

Heat conduction in a free-standing chemical vapor-deposited polycristalline diamond film has been investigated by means of combined front and rear photoacoustic signal detection techniques and also by means of a “mirage” photothermal beam deflection technique. The results obtained with the different techniques are consistent with a value of α=(5.5±0.4)×10⁻⁴ m² · s⁻¹ for thermal diffusivity, resulting in a value ofκ=(9.8±0.7)×10² W·m⁻¹·K⁻¹ for thermal conductivity when literature values for the density and heat capacity for natural diamond are used.