Plastic behaviour of Cd x Hg1−x Te (0⩽ x⩽1) crystals

Cd _x Hg_1–x Te (0x1) single crystals were strained by microhardness and by constant strain rate uniaxial compression tests, in the temperature range 300 to 600 K. Hardness curves as function of temperature can be described by empirical relations. Stress-strain curves, relaxation tests and dislocation observations using transmission electron microscopy show that the deformation is controlled by a thermally activated Peierls mechanism. Moreover, dislocations are dissociated with a stacking fault energy which does not depend on thex composition.     

Phase relation in the system La1−xBaxFeO3−y (0⩽x⩽0.70)

Samples of the system La_1–xBa_xFeO_3–y, (0x0.70) have been synthesized and investigated by means of X-ray diffraction and Mössbauer effect. Two different phases, i.e. a barium-poor orthorhombic perovskite phase and a barium-rich cubic perovskite phase, were found to exist in the system. The phase relation at room temperature is presented.     

Carbon monoxide oxidation on (Mg6−x Al x )MnO8 (0⩽x⩽0.6)

Murdochite-type (Mg_6–x Al _x )MnO_m8 (0x0.6) was synthesized at low temperature (700 °C) with the sol-gel process. The specific surface area, crystallite size, catalytic activity for the CO oxidation, and adsorption isotherms of oxygen on (Mg_6–x Al _x )MnO₈ were measured. The increase of the specific surface area with increasing Al³⁺ ion content was explained by the decrease of the particle size. The catalytic activity increased with increasing Al³⁺ ion content, and this increase was caused by the valence deviation from the Mn⁴⁺ ion to the Mn^3.5+ ion.     

Electrical transport in new La1−xNdxTlO3 (0 ⩽x⩽ 1) system

The electrical conductivity () and thermoelectric power (S) for the system La_1–x Nd _x TlO₃ (0 x 1.0) in the temperature range 295 to 805 K are reported. Both log andS as a function ofT have been found to be linear with a break in the slope around a specific temperature,T _B. The break temperature systematically decreases as we proceed from the systemx=0 tox=1.0. It has been concluded that conduction belowT _B is extrinsic and takes place owing to hopping of electrons localized on the defect centre Tl²⁺ to Tl³⁺ on normal sites. Conduction aboveT _B is the normal band type in all systems. The energy band gap has been evaluated in all cases and it has been found that it decreases systematically fromx=0 tox=1.0.     

Formation and characterization of the solid solutions (CrxFe1−x)2O3, 0⩽x⩽1

The solid solutions (Cr_xFe_1–x)₂O₃, 0 x 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, Mössbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, -(Cr_xFe_1–x)₂O₃, which is isostructural with -Fe₂O₃ and phase C, which is closely related to Cr₂O₃. Phase F exists in samples heated up to 900°C, for 0 x 0.95. Phase C exists from x0.27 to x=1 for samples heated up to 900°C and from x0.65 to x=1 for samples heated up to 1200 °C. For samples heated up to 900 °C, the solubility limits were 27.5 ± 0.5 mol% of Cr₂O₃ in -Fe₂O₃ and 4.0 ± 0.5 mol % of -Fe₂O₃ in Cr₂O₃. For the samples heated at 1200 °C the diffraction peaks for the F and C phases in the two phase region were severely overlapped and thus the solubility limits could not be determined accurately as for previous samples. ⁵⁷Fe Mössbauer spectra of the samples heated up to 1200 °C showed significant broadening of spectral lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x0.7, a paramagnetic doublet with collapsing sextet was observed. The spectra were interpreted in terms of an electronic relaxation effect; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect could not be excluded. The FT-IR spectra showed transition effects in accordance with the X-ray diffraction results. The most intense absorption bands, observed for the samples heated up to 1200 °C, were located at 460 and 370 nm (22 000 and 27 000cm^–1) for x 0.5, 500 and 360 nm for x < 0.3, and might be correlated with the strong enhancement of the pair transitions through antiferromagnetic interactions. The intensification of the ⁶A₁ 4T₁ Fe³⁺ ions in all spectra and the development of the absorption at 13000 cm^–1 due to a metal-metal charge transfer (Cr³⁺ Fe³⁺) transition, might be explained by exchange coupling which has been observed in some spinel compounds.     

Thermoelectric properties of Bi1−xSbx films with 0 < x ⩽ 0.3

The electrical conductivity, its temperature coefficient and the thermoelectric power of Bi_1−xSb_x films with 0 < x ⩽ 0.3 and thicknesses from 20 to 400 nm were measured in the temperature range 80–400 K. The results are discussed in the framework of a previously proposed anisotropic non-degenerate two-band model.     

Structural properties of nickel manganite Ni x Mn3−x O4 with 0.5 ⩽x ⩽ 1

Single-phase nickel manganite spinels, Ni _x Mn_3–x O₄, with 0.5 x 1, were prepared by a careful thermal processing of nickel-manganese coprecipitated oxalate precursors. Powder X-ray diffraction analysis of the spinel revealed the presence of cubic single spinel phase with parametera which decreases with nickel content. The lattice parameter variation can be explained in terms of the distribution of Ni²⁺ ions on the octahedral sites. Therefore, a fine analysis of data shows that some Ni²⁺ ions (forx>0.56) are located in tetrahedral sites. The percentage of nickel in A-sites increases with nickel content (x) following the relation % Ni²⁺ in A sites =P = – 82.1x ²+192.4x–81.5 and thus the general formula for cation distribution is

Structural studies of compounds in the series GaSxSe1−x (0⩽x⩽1) grown by iodine vapour transport

A discontinuity in the length of thec-axis of compounds in the series GaS _x Se_1–x ) is observed at the compositionx=0.25. This is thought to be caused by a transition from the structure of GaS to the structure of GaSe. Although lattice parameter measurements indicate that the transition is abrupt, structure factor calculations and observations of the form of the (0 0 0 1) surface growth features indicate that the transition is not sharp, but takes place over the composition range 0.2x0.3. Growth features change in form asx varies, from hexagonal spirals characteristic of GaS to triangular spirals typical of GaSe.     

Synthesis and structural characterization of solid solutions: Li3x La(1−x)VO4 (0⩽x⩽0.3), monazite-type

Li_3x La(_1–x )VO₄(0x0.3) solid solutions have been obtained by thermal treatment of lanthanum and lithium nitrates with V₂O₅ in the temperature range 700–980 K. The crystal structure of these single phases has been refined by the Rietveld analysis of powder X-ray diffraction data. The structure refinement of Li_0.15La_0.95VO₄ by neutron diffraction has been also achieved at 295 K. This compound adopts a distorted monazite-type structure: space group P2₁/n, a=0.7047(1) nm b=0.7283(6) nm c=0.6726(8) nm, =104.86(1)°, Z=4.     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.     

Dielectric properties of the system Ca1−xYxTi1−xCoxO3(0.00 ⩽ x ⩽ 0.15)

The dielectric behaviour of the compositions withx0.15 in the system Ca_1–x Y _x Ti_1–x Co _x O₃ sintered and cooled in air has been studied. Space-charge polarization which arises due to the presence of chemical inhomogeneities at the micro-level contributes significantly to their dielectric constant. The composition with x=0.05 exhibits temperature and frequency-independent dielectric constant and very small dielectric loss.     

The preparation,characterization and electrical properties of copper manganite spinels,CuxMn3−xO4, 0 ⩽x ⩽ 1

Single-phase copper manganite spinels Cu _x Mn_3–x O₄ with 0x1 were prepared by a careful thermal processing of copper-manganese co-precipitated hydroxide precursors. Powder X-ray diffraction (XRD) analysis of these spinels revealed the presence of a tetragonally distorted single spinel phase, with tetragonal distortionc/a > 1 which decreases with copper content. Thermogravimetric analysis (TGA) curves, run in an oxygen atmosphere for all the compositions studied, are characterized by a stability step up to 250 to 300° C, followed by a domain of oxidation between 300 and 900° C and finally a domain of reduction that restores the initial stoichiometry of the samples. The oxidation is observed to occur in two successive steps. The phenomenon appearing at the low temperature is due to the oxidation of Cu⁺ ions, while that at higher temperature corresponds to the oxidation of Mn²⁺ ions in tetrahedral sites. Further, electrical resistivity measurements confirm the presence of Cu⁺ ions on the tetrahedral sublattice of spinel. Correlation of the results obtained by XRD, TGA and electrical resistivity measurements permits one to infer the cation distribution, given by Cu _x ⁺ Mn _1–x ²⁺ [Mn _2–x ³⁺ Mn _x ⁴⁺ ] O ₄ ^2– .     

Metastability of the K2NiF4 type structure of the solid solution LaCa(Cr x Al1−x )O4(0⩽x⩽0.10)

Metastability of the K₂NiF₄ type aluminate LaCaAlO₄ and its chromium diluted solid solution LaCaCr _x Al_1–x O₄ (x0.10) was evidenced at 1400C in air, in terms of demixing into the parent structures of the 11 intergrowth, i.e. the perovskite and rocksalt type LaAlO₃ (LaCr _x Al_1–x O₃) and CaO, respectively. This behaviour is discussed comparatively with YCaAlCO₄ and LaSrAlO₄ whose structures are stable under the same thermodynamic conditions. The results of a structure analysis are used to emphasize the role of the nine-fold co-ordination of the (A ³⁺=Y³⁺, La³⁺; A²⁺=Ca²⁺, Sr²⁺) cations as mixing the twelve-fold co-ordination of A ³⁺ in A ³⁺AlO₃ perovskite and the six-fold one of A ²⁺ in A ²⁺O rocksalt. Calcium-oxygen underbonding in the (La, Ca)-O-Al bridge is assumed to trigger the metastability of the intergrowth structure at high temperature.     

Structural,thermal and transport studies on Ag1 − x Cuxl (0.05 ⩽ x ⩽ 0.25) solid electrolyte

Preparation and characterization studies on polycrystalline samples of Ag_{1 – x}Cu_xl wherex=0.05, 0.1, 0.15, 0.2 and 0.25, respectively, have been reported. Samples were analysed using powder X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques in order to identify the compositions and phase transition temperatures. A.c. electrical conductivity studies were carried out on pelleted specimens of various compositions in the frequency range 65.5 kHz to 1 Hz and over the temperature range 293–412 K. DSC results obtained in the temperature range 373–473 K have shown that the ß- to -phase transition temperature is enhanced from 426 K to 438 K whenx is increased from 0.05 to 0.25. XRD results have indicated that there is a shift ind-spacing when the Cul content is increased, suggesting changes in the crystal structure. Typical XRD patterns recorded for the composition Ag_0.95Cu_0.05l at three different temperatures (room temperature, 373 and 473 K, respectively) have confirmed that both face-centred cubic and hexagonal phases would be present at room temperature and at 373 K as well, whereas at 473 K the structure would be purely body-centred cubic in nature. A.c. impedance analysis of the above samples appears to suggest that their electrical conductivity, predominantly due to the migration of Ag⁺ ions, lies in the order of 10^–4S cm^–1 at room temperature.     

A new ordered sold solution with a bixbyite structure: The compounds Cu2+xTi2−xFe2−xSbxO9 (0 ⩽ x ⩽ 1.4)

A new solid solution with the formula Cu_2+xTi_2−xFe_2−xSb_xO₉ was prepared by solid state reaction in air at 900°C. A rather large homogeneity range is observed: 0 ⩽ x ⩽ 1.4. The X-ray powder diffraction shows a (Fe, Mn)₂O₃ bixbyite type structure with a cubic elementary cell. The a parameter increases with the Cu⁺² amount. Two types of polyhedra are present with on ordered cationic distribution over them. Cu⁺² exhibits a highly distorted octahedral coordination: PII sites and Sb⁺⁵ an almost regular one: PI sites. The octahedral distortion is discussed in terms of two parameters: the bond length deviation Δoct and the bond angle variance σ² oct. The stabilization of the bixbyite structure is well understood in the context of a strong correlation between Δoct of the PII polyhedra and σ²oct of the PI polyhedra.     

Electrical conduction in γ-irradiated and unirradiated Fe3O4, CdFe2O4 and Co x ZN1−x Fe2O4 (0 ⩽x ⩽ 1) ferrites

The electrical conductivity of -irradiated and unirradiated finely divided ferrites of composition Fe₃O₄, CdFe₂O₄ and Co _x Fn_1–x Fe₂O₄(0 x 1) was studied in a nitrogen atmosphere as a function of temperature. Fe₃O₄, ZnFe₂O₄ and CdFe₂O₄ showed n-type conduction, whereas CoFe₂O₄ showed p-type conduction. For Co _x Zn_1-x Fe₂O₄ it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe₃O₄, and Co _x Zn_1–x Fe₂O₄(0 x 1) was explained by a hopping mechanism, whereas the conduction in ZnFe₂O₄ and in CdFe₂O₄ is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of -irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.     

Crystallographic and morphological characterization of sprayed Cd1−yZnyS thin films for 0 ⩽ y ⩽ 0.3

In this paper we present our results on the characterization of Cd_1−yZn_yS films prepared by spray pyrolysis. It is shown that a degradation of the crystallinity appears when the zinc content is increased.     

Pb1−x Bi x /Bi/Pb1−x Bi x Josephson junction

A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb_1–x Bi _x (0x 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses inÅ and bismuth weight ratiosx. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratiosx at the temperature of 4.2 K.     

Lattice-matched epitaxial Pb1 − x Mn x Se/PbSe1 − x S x heterojunctions

This paper examines the possibility of producing lattice-matched p-n heterojunctions based on epitaxial n-Pb_{1 ? x} Mn _x Se (x = 0.02) and p-PbSe_{1 ? x} S _x (x = 0.04) films. The heterojunctions have been grown by molecular beam epitaxy in a single processing cycle, without breaking the vacuum, using a compensating Se vapor source in the growth process. Optimal conditions have been found for the growth of structurally perfect (W _1/2 = 90″-100″) epitaxial films and fabrication of lattice-matched heterojunctions based on such films, photosensitive in the IR spectral region.     

High-Pressure Studies on Superconductivity in LaFeAsO1−x F x and SmFeAsO1−x F x

The pressure dependence on the superconducting transition temperature (T _c ) was investigated for the iron-based superconductors LaFeAsO_1−x F _x and SmFeAsO_1−x F _x . The T _c ’s increase largely for LaFeAsO_1−x F _x with a small increase of pressure, while a sharp decrease of T _c was observed for SmFeAsO_1−x F _x . The electrical resistivity measurements reveal pressure-induced superconductivity for undoped LaFeAsO and SmFeAsO. These pressure effects seem to be related to an anisotropic decrease of the lattice constants under high pressure from the x-ray diffraction measurements up to 10 GPa for the LaFeAsO_1−x F _x system.