Nernst effect of stripe ordering La<Subscript>1.8−x</Subscript>Eu<Subscript>0.2</Subscript>Sr<Subscript>x</Subscript>CuO<Subscript>4</Subscript>

We investigate the transport properties of La_1.8−xEu_0.2Sr_xCuO₄ (x = 0.04, 0.08, 0.125, 0.15, 0.2) with a special focus on the Nernst effect in the normal state. Various anomalous features are present in the data. For x = 0.125 and 0.15 a kink-like anomaly is present in the vicinity of the onset of charge stripe order in the LTT phase, suggestive of enhanced positive quasiparticle Nernst response in the stripe ordered phase. At higher temperature, all doping levels except x = 0.2 exhibit a further kink anomaly in the LTO phase which cannot unambiguously be related to stripe order. Moreover, a direct comparison between the Nernst coefficients of stripe ordering La_1.8−xEu_0.2Sr_xCuO₄ and superconducting La_2−xSr_xCuO₄ at the doping levels x = 0.125 and x = 0.15 reveals only weak differences. Our findings make high demands on any scenario interpreting the Nernst response in hole-doped cuprates.     

Microwave characterization of Pb<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> multiferroics at X-band

The microwave characteristics of Pb_1?x Ca _x Fe_0.5Nb_0.5O₃ multiferroics (x = 0.0, 0.4, 0.45, 0.5, 0.55, 0.6), have been investigated as a function of frequency and substitution. The results depict ?13.99 dB reflection loss at 11.65 GHz in composition x = 0.6. Microwave absorption is enhanced with substitution of Ca²⁺ ions and undoped composition 0.0 behaves as electromagnetic shield. The model governing microwave absorption is discussed and different compositions for electromagnetic applications have been suggested.     

Optical activity of γ<Subscript>1</Subscript>-(Ga<Subscript>x</Subscript>In<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>Se<Subscript>3</Subscript> crystals

The optical activity of uniaxial γ₁-(Ga_xIn_1?x )₂Se₃ crystals (x=0.1, 0.2, 0.3, 0.4) is studied at T=295 and 77 K in the spectral range 0.5–0.8 πm. It is found that the cationic substitution In → Ga leads to a nonlinear increase in the specific rotation of the plane of polarization ρ and the component g ₃₃ of the gyration tensor. It is shown that the gyrotropy of the crystals studied is determined by high-energy transitions whose energy exceeds the energy of the edge transitions and that the gyrotropy observed has a molecular origin.     

Magnetocaloric properties of manganites La<Subscript>1−x</Subscript>(Ag,K)<Subscript>x</Subscript>MnO<Subscript>3</Subscript>

The temperature and magnetic-field dependences of the magnetocaloric effect in manganites La_1−x Ag _x MnO₃ (x = 0.1; 0.15; 0.2) and La_1−x K _x MnO₃ (x = 0.1; 0.11; 0.13; 0.15; 0.175) were studied by a direct method. Large changes in the sample temperature were detected as a magnetic field changed by ΔH = 10 kOe. Temperatures of the magnetocaloric effect maxima are near room temperatures. Field dependences of the magnetocaloric effect show no signs of saturation in fields to 30 kOe.     

Dielectric properties of CuInP<Subscript>2</Subscript>(Se<Subscript>x</Subscript>S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>6</Subscript> solid solutions

The dielectric properties of layered crystals of CuInP₂(Se_xS_1?x)₆ solid solutions are studied at x = 0.02, 0.05, 0.20, and 0.40. At a low selenium content (x ≤ 0.05), the solid solutions undergo a transition to the phase with short-range polar order. This transition manifests itself as a diffuse maximum in the temperature dependence of the permittivity ε′(T). Ferroelectric ordering in the solid solutions under investigation is suppressed at x > 1. It is assumed that the structural disordering initiated by the substitution of atoms in the anion sublattice of the solid solutions at 0.1 < x < 0.75 leads to the formation of the state of structured glass. The dielectric relaxation dispersion observed in the radio-frequency range at temperatures of 80–140 K is associated with the freezing of the relaxation dynamics of individual copper atoms.     

Thermal expansion of (Sr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>x</Subscript>)<Subscript>3</Subscript>Ru<Subscript>2</Subscript>O<Subscript>7</Subscript> single crystals at low temperatures

For single-crystal samples of the (Sr_1?xLa_x)₃Ru₂O₇ ruthenates, the temperature dependence of the thermal expansion coefficient α(T)) is measured in the range 4.2–80 K. The effect of magnetic fields H ≤ 3.5 T on thermal expansion is analyzed. It is found that the (Sr_1?xLa_x)₃Ru₂O₇ ruthenates exhibit an anomalous (negative) thermal expansion coefficient in the temperature range T ≤ 18 K. The position and width of the anomaly revealed in the temperature dependence of the thermal expansion coefficient α(T)) depend substantially on the magnetic field. The origin of the thermal expansion anomaly in ruthenates, the correlation of this anomaly with the stability of the crystal lattice, and the common nature of the anomalies in the thermal properties of ruthenates and high-temperature superconductors are discussed.     

Influence of Zn/Co ratio on dielectric behavior of Na<Subscript>2</Subscript>Zn<Subscript>1 ‐ x</Subscript>Co<Subscript>x</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> glasses

A series of zinc phosphate glass doped with cobalt Na₂Zn_(1???x)Co_xP₂O₇ (x = 0, 1, 2 and 5 mol%) was synthesized. These glasses were characterized by both infrared and large broadband dielectric spectroscopy. Infrared spectra indicate the increase of Zn/Co ratio creates defect in phosphate network due to the depolymeration of phosphate anions. The dc conductivity increases and activation energy decreases with the amount of cobalt ions in the glass network. The impedance measurements reveal that the total conductivity follows Jonscher’s power law. The dielectric constant and dielectric loss increased with the temperature and decreased with the frequency whatever the cobalt proportion.     

Spectroscopic study of magnetic phase transitions in Nd<Subscript>x</Subscript>Gd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Magnetic ordering and spin reorientation in iron borates Nd_xGd_1?xFe₃(BO₃)₄ (x = 0.01, 0.04, 0.25, 1.0) are studied using a rare-earth spectroscopic probe.     

Heat capacity of the Pb<Subscript>5</Subscript>(Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>)<Subscript>3</Subscript>O<Subscript>11</Subscript> ferroelectric system

The temperature dependences of the molar heat capacity at constant pressure, C_p, of Pb₅(Ge_1?xSi_x)₃O₁₁ crystals with x=0, 0.39, and 0.45 in the range 5–300 K, as well as of their permittivity, dielectric losses, and the pyroelectric effect, have been measured. Experimental data on the temperature behavior of the heat capacity are presented in the form of a sum of two Debye and one Einstein terms, C_p(T)=0.405C_D1(Θ_D1=160 K, T)+0.53C_D2(Θ_D2=750 K, T)+0.046C_E(Θ_E=47 K, T). Besides a peak in the region of the ferroelectric Curie point T_c=450 K for crystals with x=0, the temperature dependences of the heat capacity did not reveal any other pronounced anomalies.     

Correlation between raman spectra and structural properties of Zn<Subscript>2 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>x</Subscript>In<Subscript>x</Subscript>Se<Subscript>2</Subscript> films

The Raman spectra of Zn_{2 ? 2x} Cu_xIn_xSe₂ (ZCIS) semiconductor films designed for use as optically active layers in thin-film solar cells have been investigated. The Raman spectra of ZCIS films are characterized by the presence of the dominant mode A ₁, which is observed in A^IB^IIIC ₂ ^VI compounds with chalcopyrite structure. The spectra of CuInSe₂ films (x = 1) obtained at low temperatures (T ≤ 400°C) contain and additional mode at 258 cm^?1, which is due to the presence of the impurity Cu_xSe phase. All modes observed in the spectra of ZCIS films with a Zn concentration ≤20 at % obtained under optimal conditions (520–540°C) correspond to the symmetry of vibrations in the chalcopyrite structure. The broadening and blue shift of the A ₁ mode occurring with an increase in the Zn concentration are indicative of degradation of the chalcopyrite crystal structure and the chalcopyrite → sphalerite phase transition at Zn concentrations exceeding 20 at %.     

Transformation of dielectric properties and appearance of relaxation behavior in Pb<Subscript>5</Subscript>(Ge<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>x</Subscript>)<Subscript>3</Subscript>O<Subscript>11</Subscript> crystals

The special features of the dielectric properties and conduction of ferroelectric crystals of Pb₅(Ge_1?xSi_x)₃O₁₁ (0 ≤ x ≤ 0.67) solid solutions were studied. Permittivity anomalies close to the temperatures T₁ ≈ 260 K and T₂ ≈ 130 K, the appearance of relaxator behavior at x > 0.35, and critical behavior of the concentration dependences of dielectric and pyroelectric characteristics at x₁ = 0.35 and x₂ = 0.60 were observed and studied. These phenomena were found to be related to the dynamics of charge localization on defects with activation energies of U_a1 ≈ 0.6 eV and U_a2 ≈ 0.23 eV. Relaxator behavior appears when the Curie point lies in the temperature region of thermal charge localization. The concentration dependence features at x₁ and x₂ are explained by the coincidence of the Curie point and the centers of the temperature regions of charge localization on the U_a1 and U_a2 defect levels, respectively.     

Spectral-luminescent properties of AgLa<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> solid solutions

The luminescent properties of AgLa_{1 − x} Eu _x (MoO₄)₂ (x = 0.1, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) under laser excitation (λ = 337.1 nm) are studied. It is shown that, upon substitution of Eu³⁺ for La³⁺, the symmetry of luminescence centers does not vary. According to the X-ray diffraction data, all samples have scheelite-like structure; the pattern of variation in volumes of their unit cells counts in favor of the presence of a continuous series of solid solutions. It is found that an increase in the europium concentration in AgLa_{1 − x} Eu _x (MoO₄)₂ leads to an increase in the luminescence intensity with a maximum at x = 0.9.     

Magnetorefractive effect in (Co<Subscript>50</Subscript>Fe<Subscript>50</Subscript>)<Subscript>x</Subscript>(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> granular films

The reflectivity spectra and the magnetorefractive effect (MRE) of (Co₅₀Fe₅₀)_x(Al₂O₃)_1?x metal-dielectric granular films (0.07<x<0.52) are analyzed in the IR spectral range λ=2.5–25 µm. It is revealed that the specific features observed in the spectra at λ≈8.5 and 20 µm are associated with the excitation of phonon modes in the dielectric matrix. The magnetorefractive effect in the films is observed below the percolation thresh-old only in p-polarized light and above the percolation threshold for both the p and s polarizations. It is demonstrated that the optical properties of (Co₅₀Fe₅₀)_x(Al₂O₃)_1?x films in the IR spectral range, to a first approximation, can be interpreted in the framework of the effective-medium theory and the magnetorefractive effect can be explained in terms of the modified Hagen-Rubens relation.     

Fractal magnetic microstructure in the (Co<Subscript>41</Subscript>Fe<Subscript>39</Subscript>B<Subscript>20</Subscript>)<Subscript>x</Subscript>(SiO<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> nanocomposite films

Magnetostructural methods are applied to determine the exchange bond percolation limit in (Co₄₁Fe₃₉B₂₀)_x(SiO₂)_1?x nanocomposites (x _c = 0.30 ± 0.02), which separates the phase plane along the metal concentration axis into a superparamagnetic region and a ferromagnetic region. It is shown that, with respect to the singularities of the magnetization up to the magnetization saturation curves, the ferromagnetic region is further subdivided into three regions differing in the character of the spatial propagation of the magnetization ripples or in the magnetic correlation function characteristics. The fractal dimension of the nanocomposite magnetic microstructure near the percolation threshold is determined.     

Spectral-luminescent properties of LiRbLa<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Eu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>(MoO<Subscript>4</Subscript>)<Subscript>4</Subscript> solid solutions

The luminescent properties of LiRbLa_{2 − x} Eu _x (MoO₄)₄ (x = 0.002, 0.02, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0) solid solutions are investigated under laser excitation {λ_ex = 337.1 nm). It is established that the composition containing 50 at % Eu³⁺ is the brightest of the considered set of phosphors and has the highest quantum yield.     

Influence of the technique of preparation of (Co)<Subscript>x</Subscript>(LiNbO<Subscript>3</Subscript>)<Subscript>100 − <Emphasis Type="Italic">x</Emphasis></Subscript> nanocomposites on their magnetic properties

The field and concentration dependences of the ferromagnetic resonance spectra and static magnetic parameters of granular Co_x(LiNbO₃)_{100 ? x} nanocomposites (26 ≤ x ≤ 81 at %) with a matrix of amorphous ferroelectric LiNbO₃ have been investigated. It is shown that oxidative processes affect the magnetic parameters of this material.     

Effect of substrates on the morphology of Ba<Subscript>x</Subscript>Sr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> nanometer-scale films

The initial stages in the growth of Ba_xSr_1?xTiO₃ films on various dielectric substrates were studied using the middle-energy ion scattering spectroscopy, and the results obtained were used to analyze microdefects in the film. The character of film growth was found to depend on the shape, size, and electrostatic state of crystallographic unit cells of the substrate surface. The growth was epitaxial on an SrTiO₃ substrate. The film prepared on an LaAlO₃ substrate consists of slightly disordered crystallites. Films on MgO substrates demonstrated island-type growth up to a thickness of 20 nm, with foreign phases observed to form; as the film thickness increased, the growth acquired an epitaxial pattern. The film grown on the \(\alpha - Al_2 O_3 (1\bar 102)\) surface was polycrystalline and contained textured blocks.     

Synthesis of compositionally controllable Cu<Subscript>2</Subscript>(Sn<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript>)S<Subscript>3</Subscript> nanocrystals with tunable band gaps

In this work, we show that compositionally controlled Cu₂(Sn_1–xGe_x)S₃ nanocrystals can be successfully synthesized by the hot-injection method through careful tuning the Ge/(Sn+Ge) precursor ratio. The band gaps of the resultant nanocrystals are demonstrated to be linearly tuned from 1.45 to 2.33 eV by adjusting the composition parameter x of the Ge/(Sn+Ge) ratio from 0.0 to 1.0. The crystalline structures of the resultant NCs have been studied by the X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), select area electron diffraction (SAED), and Raman spectroscopy. A ligand exchange procedure is further performed to replace the native ligands on the surface of the NCs with sulfur ions. The photoresponsive behavior indicates the potential use of as-prepared Cu₂(Sn_1–xGe_x)S₃ nanocrystals in solar energy conversion systems. The synthesis of compositionally controlled Cu₂(Sn_1–xGe_x)S₃ nanocrystals reported herein provides a way for probing the effect of Ge inclusion in the Cu-Sn-S system thin films.     

Infrared diffuse reflectance spectra of micropowders of Ni<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The results of experimental studies of the IR diffuse reflectance spectra in the range from 4000 to 50 cm^–1 of Ni_1–xZn_xFe₂O₄ ferrite micropowders with different concentrations of nickel and zinc are presented. The dependence of the intensity of the IR spectra of these ferrites on the changing concentrations of Fe²⁺ and Fe³⁺ cations in ferrites of different compositions is found. The features of change of the reflectance spectra are studied depending on the ferrite compositions, and an interpretation of the observed spectral structures is proposed.     

Growth and photoelectric properties of graded-gap Si-(Si<Subscript>2</Subscript>)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(GaP)<Subscript>x</Subscript> heterostructures

Theoretical grounds for formation of continuous substitutional solid solutions are analyzed taking into account the generalized moments, the difference in valence, and covalent radii of initial components. On the basis of these studies, the technology of formation of epitaxial (Si₂)_1?x(GaP)_t (0≤x≤1) layers on silicon substrates from the tin solution-melt using forced cooling is developed. The distribution of components over the thickness of Si-(Si₂)_1?x(GaP)_x layers, the photosensitivity, and the current-voltage characteristics of the Si-(Si₂)_1?x(GaP)_x heterostructures are studied. Analyses of the results of the X-ray studies and photoelectric properties of obtained solid-solution epitaxial layers indicate that the grown graded-gap (Si₂)_1?x(GaP)_x layers have a high structural quality.