Appearance of Griffiths Phase in La0.7−x Pr x Ba0.3MnO3 (0 ≤x≤ 0.2)

Polycrystalline La_0.7?x Pr _x Ba_0.3MnO₃ (0 ≤x≤ 0.2) samples were prepared using solid-state reaction and checked by X-ray diffraction. Magnetization measurements versus temperature and applied magnetic field were used to investigate their magnetic properties. For samples with x= 0.2, the Griffiths phase is observed when the inverse of susceptibility (1/ χ vs. T) is analyzed.     

Conduction in nanostructured La1?x Sr x FeO3 (0 ≤ x ≤ 1)

We investigated electrical properties of nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) from 300 K?C400 K. The nanostructured La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO₃ with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ?? 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO₃ from 300 K?C400 K. The experimental values of field-lowering coefficient were by 2.56?C6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe⁴⁺ ions in addition to Fe³⁺ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La_1?x Sr _x FeO₃ (0 ?? x ?? 1) was also carried out in the temperature range from 300 K?C400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La_0.9Sr_0.1FeO₃.     

Transport Properties of Ca1 – x MnO3 – δ + xCeO2(0 < x ≤ 0.15) Mixtures

Data are presented on the temperature-dependent electrical conductivity and thermoelectric power of Ca_{1 – x} MnO_{3 –} + xCeO₂ (0 < x 0.15) mixtures obtained as intermediate products in the synthesis of Ca_{1 – x} Ce _x MnO_{3 –} solid solutions. The electrical properties of the mixtures are shown to be dominated by those of the perovskite-like phase Ca_{1 – x} MnO_{3 –} and to depend on Ca concentration. All of the samples with 0 x 0.15 exhibit n-type conductivity. The charge transport in CaMnO_{3 –} below 930 K is attributable to small-polaron hopping. At higher temperatures, conduction through delocalized states seems to prevail. In the Ca_{1 – x} MnO_{3 –} + xCeO₂ mixtures with 0.05 x 0.15, small-polaron hopping is observed between 160 and 920 K. Below 160 K, the temperature variation of conductivity in the samples with x = 0.1 and 0.15 follows Mott's law.     

Phase diagram of the CrxVSe2 system (0 ≤ x ≤ 1.0)

The phase diagram of the pseudo-binary CrVSe₂ (i.e. Cr_xVSe₂) system was determined by means of X-ray and DTA measurements, in the composition range 0≤x≤1.0. As the results, the following 6 phases have been confirmed to be existent in the temperature range 300≤T≤1100 : CdI₂,M₅X₈,M₃X₄,α,NiAs and Cr. Among them, M₅X₈,M₃X₄ and α phases undergo a phase transition to the CdI₂- or NiAs-type structures at high temperatures. The α phase (0.825≤x≤0.875 at 500°C) is a new phase firstly confirmed by this study.     

Neutron investigation of Nd2-x-yCexLayCuO4 (0≤x≤0.2; y=0.5,1)

Samples of the electron-doped superconductor precursor Nd_2-x-yCe_xLa_yCuO₄ with 0x0.2 and y=0.5, I have been synthesized with a sol-gel method. While the as-prepared samples are in the normal state, oxygen reduction results in superconducting samples. The dependence of T_c upon Ce-doping x and oxygen content (4-) was determined in detail. It turned out that the internal pressure exerted by the La ions results in an extended superconducting range in x and compared to Nd_2-xCe_xCuO_4- Elastic neutron scattering was used to investigate the dependence of structural features upon doping. Upon oxygen reduction a non-isotropic shrinking of the unit cell (lattice parameter a increases, c decreases) and indications for interstitial oxygen were found. The local electronic surrounding of the Nd ions was observed via the crystal-field splitting by inelastic neutron scattering and turned out to be inhomogeneous. Such electronic inhomogeneities were previously measured for other high-T_c superconductors.     

Thermal Properties of La1−x A x CoO3 (A = Ca and Ba)

The thermal properties of La_1?x A _x CoO₃ (A = Ca, Ba and 0.0≤x≤0.3) for temperature (1 K≤T≤300 K) have been investigated using the Modified Rigid ion model (MRIM) with pair wise interionic interaction potential. The temperature dependent (1 K≤T≤300 K) variation of specific heat and thermal expansion for La_1?x A _x CoO₃ (A = Ca, Ba and 0.0≤x≤0.3) has presented proper interpretation of the experimental data. Also the effect of lattice distortions on the thermal properties of these perovskite cobaltates has been studied by an atomistic approach. In addition, the results on the cohesive energy (?), molecular force constant (f), Reststrahlen frequency (υ), Debye temperature (θ _D ) and Gruneisen parameter (γ) are also discussed.     

Electrochemical,optical, and magnetic properties of Ni x InSe (0 < x ≤ 1) intercalation compounds

We have studied the electrochemical, optical, and magnetic properties of nickel-intercalated InSe single crystals. The energy position of the excitonic maximum and the full width at half maximum of the excitonic band in the Ni _x InSe intercalation compounds have been shown to be nonmonotonic functions of nickel concentration. Nickel-intercalated InSe possesses ferromagnetic properties: the dependence of its magnetic moment on magnetic field has the form of a hysteresis loop, characteristic of hard-magnetic ferromagnets.     

Negative Photoconductivity in TlIn1 –xNdxSe2(0 < x≤ 0.05) Solid Solutions

TlIn_{1 – x} Nd _x Se₂(0 < x 0.05) solid solutions were found to exhibit negative photoconductivity due to changes in the charge state of recombination centers upon carrier injection from the electrical contacts. The transient behavior of negative photoconductivity in TlIn_{1 – x} Nd _x Se₂was found to be composition-independent.     

Phase Formation in the Course of Oxidation of In x Se1 − x Alloys (0.47 ≤ x ≤ 0.53)

We have determined the characteristic temperature ranges of heating of In _x Se_{1 – x} (0.50 x 0.52) alloys in air. We have established that the annealing of InSe powder in selenium vapors leads to the stabilization of the rhombohedral structure.     

Phase Relations in the Systems M–Mn–P (M = Cr, Mo, W, Re)

The 1070-K phase relations in the M–Mn–P (M = Cr, Mo, W; 67 at. % P) and Re–Mn–P (50 at. % P) systems were studied by x-ray diffraction. The existence of the known phosphides Mo₄Mn₆P₅ and (Mn,W)₁₂P₇ was confirmed, and a new phase with the general formula (Mn,Mo)₁₂P₇ and stoichiometry range Mo_4.6–1.8Mn_7.4–10.2P₇ was identified. Its structure was determined by powder diffraction profile analysis (R = 0.074): Cr₁₂P₇ structure type, sp. gr. P6, a = 0.94929(8) nm and c = 0.33565(3) nm for Mn_7.4Mo_4.6P₇. The Mo and Mn atoms in the structure of this phase were shown to occupy all positions at random. In addition to the known solid solutions (Cr,Mn)₃P (Ni₃P structure type), (Cr,Mn)₁₂P₇ (Cr₁₂P₇), (Cr,Mn)P, and (Mn,Mo)P (MnP), we revealed new solid-solution series: (Cr,Mn)₂P (Cr₂P), (Mn,Cr)₂P (Fe₂P), (Mn,Mo)₃P (Ti₃P), (Mo,Mn)₃P (-V₃S), (Mo,Mn)P (WC), (W,Mn)P (MnP), (Mo,Mn)P₂, and (W,Mn)P₂ (MoP₂). The Re–Mn–P system was found to contain neither ternary phosphides nor solid solutions.     

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.     

Synthesis and Phase Composition of NaxMxTi8 – xO16(0.67 ≤ x≤ 2.0; M = Al, Ga, In)

The phase composition of Na _x M _x Ti_{8 – x} O₁₆(M = Al, Ga, In) materials was studied by x-ray diffraction. In the Al system, a hollandite phase was obtained in the composition range 0.67 x 2.0. The results are interpreted in terms of Goldschmidt's tolerance factor. It is shown that A₂B₈O₁₆compounds with the hollandite or Na _x TiO₂-type structure are more difficult to prepare at smaller ionic radii of M. The assumption is made that the monoclinic Na _x TiO₂-type phase may, under certain conditions, have a channel structure.     

Interdiffusion of rare-earth cations in Ln1−x ′Ln x ″ Ba2Cu3O7 − δ (Ln′, Ln″ = Y, Dy, Ho) High-T c superconductors

The Y³⁺/Ho³⁺, Y³⁺/Dy³⁺, and Dy³⁺/Ho³⁺ interdiffusion coefficients in the YBa₂Cu₃O_{7 ? δ}-HoBa₂Cu₃O_{7 ? δ}, YBa₂Cu₃O_{7 ? δ}-DyBa₂Cu₃O_{7 ? δ}, and DyBa₂Cu₃O_{7 ? δ}-HoBa₂Cu₃O_{7 ? δ} systems have been determined in air at a temperature of 1233 K by the Boltzmann-Matano method from the yttrium/holmium, yttrium/dysprosium, and dysprosium/holmium concentration profiles across the diffusion zone between two pellets of the high-T _c superconductors. The composition dependences of the interdiffusion coefficients in the solid-solution systems are presented.     

Effects of Bismuth Doping on the Physical Properties of La0.6−x Bi x Sr0.4CoO3 (0≤x≤0.15) Cobaltites

The structural and magnetic properties of cobaltites with the nominal composition La_0.6?x Bi _x Sr_0.4CoO₃ (0≤x≤0.15) have been investigated. X-ray diffraction analysis using Rietveld refinement show that all our samples crystallize in the rhombohedral structure. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT exhibits thermomagnetic irreversibility signature of short range ferromagnetic interactions in our samples. The ferromagnetic–paramagnetic transition temperature decreases with increasing Bi amount. In the paramagnetic phase, all our synthesized samples obey to the Curie–Weiss law. The Curie–Weiss analysis suggests that the spin state of Co³⁺ is IS while Co⁴⁺ ions are in IS for x=0 and LS for x≥0.05. The Bi doping also leads to a weakening in the magnetic moment. The magnetic entropy change exhibits a maximum value which decreases from 2.28 J/kg?K for x=0 to 1.24 J/kg?K for x=0.15 upon a magnetic field change of 5 T.     

Critical Behavior Near the Paramagnetic to Ferromagnetic Phase Transition Temperature in Polycrystalline La0.57Nd0.1Sr0.33Mn1?x Al x O3 (0.0≤x≤0.1)

The critical parameters provide important information concerning the interaction mechanisms near the paramagnetic to ferromagnetic transition. In this paper, we have investigated the effect of non-magnetic aluminum Al doping in Mn-site on the critical behavior in La_0.57Nd_0.1Sr_0.33MnO₃ compounds using magnetization methods near the Curie temperature T _C through various techniques such as modified Arrott plot, Kouvel?CFisher method, and critical isotherm analysis. The values of critical exponents, derived from the magnetic data yield 0.326 ??????0.366,1.265??????1.342 and 4.13 ??????5.07. The critical exponents found in this study obey the Widom scaling relation ??=1+??/??, implying that the obtained values of ?? and ?? are reliable. Experimental results have revealed that the samples exhibited the second-order magnetic phase transition with exponents which match well with those predicted for the three-dimensional Heisenberg (3D) around the critical temperature.     

Emission (Gd3+ and Sm3+) and ESR (Gd3+) studies of La1−xLnxB3O6 (Ln = Gd,Sm; 0 ≤ x ≤ 0.2 for Gd; 0 ≤ x ≤ 0.1 for Sm) phosphors

Polycrystalline powders of rare-earth doped La_1?xGd_xB₃O₆ (0?≤?x?≤?0.2) and La_1?xSm_xB₃O₆ (0.0?≤?x?≤?0.1) phosphors were successfully prepared by a B₂O₃ flux method. All the phosphor samples are well characterized by powder X-ray diffraction (XRD), infrared (IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) methods and fluorescence lifetime of Sm³⁺ ion. The XRD patterns show that La_1?xM_xB₃O₆ (M?=?Gd and Sm) adopt monoclinic with the I2/a space group. The SEM–EDS results confirmed the doping of Gd and Sm into LaB₃O₆ lattice. The IR and Raman spectra of these solid solutions gave distinctive bands corresponding to planar BO₃ and tetrahedral BO₄ groups. The photoluminescence (PL) spectra of La_1?xGd_xB₃O₆ gave a strong emission band, ⁶P_J?→?⁸S_7/2, at 310 nm. The PL spectra of La_1?xSm_xB₃O₆ phosphor showed orange-red emission at 598 nm when excited using light of wavelength of 402 nm. The results were obtained by the transition ⁴G_5/2?→?⁶H_7/2 of Sm³⁺ ions. The influence of dopant concentration on the emission profiles was studied. The ESR spectra of La_1?xGd_xB₃O₆ (x?=?0.02) gave a typical U-spectrum and spin-Hamiltonian parameters are deduced.

     

Syntheses and Magnetic-Properties of Zn-Diluted Sr-Based Perovskite Cobalt Oxides, Sr1?x Zn x CoO3; 0.05≤x≤0.3

In order to check the solubility of Zn in the (Sr_1?x Zn _x )CoO₃ perovskite structure and their research findings, several polycrystalline samples have been prepared under wide extreme synthesis conditions at 6?GPa/1300?C1650?°C. While 0.05??x??0.3 compositions revealed single phased cubic structure materials, x>0.3 showed multi-phased materials for (Sr_1?x Zn _x )CoO₃ system. Like other substituted perovskite cobalt oxide systems (Ca, Y, Ho and Ce), the transport properties of the present materials show rather sizable changes with respect to ??x??, although there are insignificant variations in lattice parameter and in Curie temperature, T _c . All the present samples show soft ferromagnetism with T _c in the range of 272?C285?K for 0.05??x??0.3. The effective paramagnetic moment, P _eff determined from the paramagnetic region decreases upon the substitution of Zn for Sr-site. These P _eff (3.3?C2.8???_B/Co) values for 0.05??x??0.3 compositions seem to suggest that the Co⁴⁺ lie in intermediate spin (IS) state for the present (Sr_1?x Zn _x )CoO₃ series, although they are slightly smaller than those expected for IS-Co⁴⁺; P _eff=3.87???_B/Co. The electrical resistivity is found to increase with increase of ??x?? for the investigated samples. The temperature and field dependence of both positive and negative magnetoresistance (MR) are noted for the Zn substituted samples. About 5% of ?CMR is observed for x=0.05 sample around the transition temperature (280?K) under the field strength difference, ??H=90?kOe. The present research findings are compared with our previous results on different perovskite cobalt oxides.     

Synthesis of (Sr1 – xCax)1 – yCuO2(0 < x< 0.86, 0 < y < 0.1) at High Pressures and Temperatures

(Sr_{1 – x} Ca _x )_{1 – y} CuO₂(0 <x< 0.86, 0 < y< 0.1) infinite-layer solid solutions were prepared at high pressures and temperatures using low-pressure, orthorhombic Sr_{1 – x} Ca _x CuO₂as a precursor, and their low-temperature magnetic susceptibility was measured.     

Synthesis and properties of LnBaFeCoO5 + δ (Ln = Nd, Sm, Gd)

LnBaFeCoO_{5 + δ} (Ln = Nd, Sm, Gd) layered oxides have been synthesized and their crystal structure, thermal stability, thermal expansion, electrical conductivity, thermoelectric power, and magnetic susceptibility have been studied. The oxides have a tetragonal structure (sp. gr. P4/mmm) with unit-cell parameters a = 0.3909(2) nm and c = 0.7695(6) nm for Ln = Nd (δ = 0.65), a = 0.3908(3) nm and c = 0.7662(6) nm for Ln = Sm (δ = 0.37), and a = 0.3908(2) nm and c = 0.7613(6) nm for Ln = Gd (δ = 0.37). The LnBaFeCoO_{5 + δ} compounds are antiferromagnetic p-type semiconductors. With decreasing Ln³⁺ ionic radius, their electrical conductivity and linear thermal expansion coefficient decrease and their thermoelectric power and antiferromagnetic ordering temperature increase. Near 518–653 K, the linear thermal expansion coefficient of the LnBaFeCoO_{5 + δ} oxides increases from (12.9–16.6) × 10^?6 to (19.3–26.5) × 10^?6 K^?1, which is due to the release of weakly bound oxygen from the oxides. We have determined parameters of charge transport in the [Fe(Co)O₂] layers in the crystal structure of the LnBaFeCoO_{5 + δ} phases.