Thermal characterization of TiC<Subscript>x</Subscript>O<Subscript>y</Subscript> thin films

Thermal wave characterization of thin films used in industrial applications can be a useful tool, not just to get information on the films' thermal properties, but to get information on structural-physical parameters, e.g. crystalline structure and surface roughness, and on the film deposition conditions, since the thermal film properties are directly related to the structural-physical parameters and to the deposition conditions. Different sets of TiC_XO_Y thin films, deposited by reactive magnetron sputtering on steel, have been prepared, changing only one deposition parameter at a time. Here, the effect of the oxygen flow on the thermal film properties is studied. The thermal waves have been measured by modulated IR radiometry, and the phase lag data have been interpreted using an Extremum method by which the thermal coating parameters are directly related to the values and modulation frequencies of the relative extrema of the inverse calibrated thermal wave phases. Structural/morphological characterization has been done using X-ray diffraction (XRD) and atomic force microscopy (AFM). The characterization of the films also includes thickness, hardness, and electric resistivity measurements. The results obtained so far indicate strong correlations between the thermal diffusivity and conductivity, on the one hand, and the oxygen flow on the other hand.     

Growth and optical properties of paraelectric K<Subscript>1-y</Subscript>Na<Subscript>y</Subscript>Ta<Subscript>1-x</Subscript>Nb<Subscript>x</Subscript>O<Subscript>3</Subscript> single crystals

We report the successful growth of an electroholographic crystal, potassium sodium tantalate niobate (KNTN), by a top-seeded solution growth method. Both blue and colorless crystals were obtained. The structure, optical absorption, and refractive dispersion properties of the as-grown crystals have been investigated. Furthermore, the Kerr coefficients R₁₁ and R₁₂ of paraelectric K_0.95Na_0.05Ta_0.61Nb_0.39O₃ single crystal were determined by using an automated scanning Mach–Zehnder interferometer. The crystal has large Kerr coefficients with R₁₁= 2.8×10^-16 m²/V² and R₁₂= -0.3×10^-16 m²/V² at the wavelength of 632.8 nm near its cubic–tetragonal phase boundary. PACS 81.10.Dn; 42.70.Nq     

Magnetic Properties of Fe<Subscript>4-y</Subscript>Al<Subscript>y</Subscript>C<Subscript>x</Subscript> Antiperovskite Compound

The crystalline structure, change of magnetization, coercive force and remanent induction of Fe_4-yAl_yC_x antiperovskite were investigated depending on the concentration of alloying elements. Correlation between atomic and magnetic ordering was established. Self-consistent calculations of the electronic structure of Fe_4-yAl_yC_x with hypothetical crystal structures close by the composition to the experimentally studied antiperovskites confirmed the necessity of taking into account non-stoichiometry of this compound. Values of the magnetic moment and the heat of formation for all the structures under investigation were calculated.     

Relations between physical properties of the biferroic Pb(Fe<Subscript>1-x</Subscript>Nb<Subscript>x</Subscript>)O<Subscript>3</Subscript>ceramics and their composition change

The work shows basic features of ferromagnetic ceramics Pb(Fe_{1 - x}Nb_x)O₃ with various contents of Fe/Nb (x=1/3, 1/2, 2/3). The synthesis were carried out by powders sintering and calcination whereas densification by hot uniaxial pressing and conventional sintering methods. Optimum conditions of PFN obtention with various contents were based on X-ray, microstructural, dielectrical and conductivity tests together with increase of iron contents in Pb(Fe_{1 - x}Nb_x)O₃ usage parameters of those ceramics worsen. Optimum parameters are shown by the ceramics with contents Pb(Fe_{1 / 2}Nb_{1 / 2})O₃ synthetized using calcination method and densified by hot uniaxial pressing method.     

Giant magnetoresistance in Hg<Subscript>1−x−y</Subscript>Mn<Subscript>x</Subscript>Fe<Subscript>y</Subscript>Te crystals

Giant magnetoresistance in Hg _1−x−y Mn _x Fe _y Te crystals is caused by clusters with “antiferromagnetic” (Mn-Te-Mn-Te, Mn-Te-Fe-Te) and “ferromagnetic” (Fe-Fe-Fe) ordering. The effect is due to the fact that the charge carriers taking part in electric current interact with the “ferromagnetic” cluster subsystem (Fe-Fe-Fe) magnetized to saturation and become spin-polarized. These spin-polarized charge carriers are strongly scattered by the “antiferromagnetic” Mn-Te-Mn-Te and Mn-Te-Fe-Te clusters, because the magnetic moments inside the clusters and resultant moments of clusters have chaotic orientations. Investigations of kinetic coefficients of Hg _1−x−y Mn _x Fe _y Te crystals before and after thermal treatment show that there is no marked correlation between the giant magnetoresistance and charge-carrier concentration, mobility, and band parameters of crystals. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 28–33, October, 2007.     

Reluctance of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>x</Subscript> oxygen-deficient ceramics

Influence of an external magnetic field on the reluctance of the YBa ₂ Cu ₃ O _x ceramics is investigated. A significant reluctance of the oxygen-deficient ceramics (with critical temperature T_c < 77 K) is established for a sample in the normal state at T < 160 K. It is demonstrated that after ceramics annealing that restores the oxygen content to a nearly optimum value, the magnetic field has essentially no effect on the sample reluctance at temperatures exceeding T_c. To explain the revealed mechanisms, a model involving ferromagnetic clusters effectively decreasing the free carrier density is used. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 68–71, April, 2007.     

Influence of dipole-dipole interactions on the angular dependence of ferromagnetic resonance spectra in arrays of Fe/Fe<Subscript>x</Subscript>O<Subscript>y</Subscript> core/shell nanocubes

We present a detailed theoretical study of the role of long-range dipole-dipole interactions on the angular dependence of ferromagnetic resonance spectra in a two-dimensional array of nanocubes. Variations of polar (φ) and azimuthal (θ) angles are studied numerically and analytically to illustrate the effect of the magnetocrystalline properties and the dipole-dipole interactions, forming complex resonance bands. In addition, we show that when the static magnetic field lies in the arrays’ plane under the angle of 129° with the edge of the array or when its tilted around 15° to the plane’s normal, the spectra of absorption transform into a plateau spanning from 0.1 T to 0.4 T, which is prominent enough for experimental observation.     

Structural and electrical properties of KCa<Subscript>2</Subscript>Nb<Subscript>5</Subscript>O<Subscript>15</Subscript> ceramics

A polycrystalline sample of KCa₂Nb₅O₁₅ with tungsten bronze structure was prepared by a mixed oxide method at high temperature. A preliminary structural analysis of the compound showed an orthorhombic crystal structure at room temperature. Surface morphology of the compound shows a uniform grain distribution throughout the surface of the sample. Studies of temperature variation on dielectric response at various frequencies show that the compound has a transition temperature well above the room temperature (i.e., 105°C), which was confirmed by the polarization measurement. Electrical properties of the material have been studied using a complex impedance spectroscopy (CIS) technique in a wide temperature (31–500°C) and frequency (10²–10⁶ Hz) range that showed only bulk contribution and non-Debye type relaxation processes in the material. The activation energy of the compound (calculated from both the loss and modulus spectrum) is same, and hence the relaxation process may be attributed to the same type of charge carriers. A possible ‘hopping’ mechanism for electrical transport processes in the system is evident from the modulus analysis. A plot of dc conductivity (bulk) with temperature variation demonstrates that the compound exhibits Arrhenius type of electrical conductivity.      

Effect of Ba-substitution on the structure and properties of Pb<Subscript>0.8</Subscript>Ba<Subscript>0.2</Subscript>[(In<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>)<Subscript>1-x</Subscript>Ti<Subscript>x</Subscript>]O<Subscript>3</Subscript> ceramics

Ferroelectric ceramics with formula Pb_0.8Ba_0.2[(In_1/2Nb_1/2)_1-xTi_x]O₃ (PBINT) (x=0.0,0.1,0.2,0.3,0.4 and 0.5) were prepared via a two-step solid state reaction method. It was found that ceramics with compositions in the range of x=0.0∼0.3 showed a pseudo-cubic structure, whereas the ceramic with x=0.5 displayed a tetragonal structure. All compositions showed significant frequency dispersion in their dielectric properties. The remanent polarization P_r as well as the coercive field E_c, measured at room temperature, increases with the Ti content. The experimental results obtained in this system are summarized into a phase diagram, with the morphotropic phase boundary (MPB) located at x=0.4. Compared with the Pb[(In_1/2Nb_1/2)_1-xTi_x]O₃ solid solution system, incorporating Ba in the A-site leads to a significant decrease in the dielectric maximum temperature T_max, a suppression of the dielectric relaxation parameter γ, and a shift of the MPB composition to a higher Ti content. PACS 77.84.Dy; 77.80.Bh; 77.22.Ch     

Impedance spectroscopy of vanadium modified BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

In recent years a wide range of Aurivillius layered materials have been introduced. These novel materials are produced in many various forms such as fibers, thin films as well as bulk by using a number of processing routes. As advanced materials they are they have many interesting properties which include a number of useful electrical properties related to separated grain and grain boundary conductivity, impedance, activation energies, etc. In this paper these properties are described and discussed in detail. The electrical properties of the vanadium doped BaBi₂Nb₂O₉ ceramic was measured over a wide range of temperatures by impedance spectroscopy (IS). The separated grain activation energy, calculated from Arrhenius characteristics at temperatures between room temperature and 600 °C, was 1 eV for 0 at.% of vanadium dopant and 1.2 eV for 10 at.%, whereas the activation energies in the grain boundary region were 0.97 and 1.15 eV, respectively. The obtained results suggest the significant role of vanadium dopant, causing ordering the crystalline structure.     

Phase transition and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)(Nb<Subscript>1-x</Subscript>Ta<Subscript>x</Subscript>)O<Subscript>3</Subscript> lead-free piezoelectric ceramics

(K_0.5Na_0.5)(Nb_1-xTa_x)O₃ lead-free piezoelectric ceramics have been prepared by an ordinary sintering technique. The results of X-ray diffraction reveal that Ta⁵⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a solid solution with an orthorhombic perovskite structure. Because of the high melting temperature of KTaO₃, the (K_0.5Na_0.5)(Nb_1-xTa_x)O₃ ceramics can be sintered at higher temperatures. The partial substitution of Ta⁵⁺ for the B-site ion Nb⁵⁺ decreases both paraelectric/cubic–ferroelectric/tetragonal and ferroelectric/tetragonal–ferroelectric/orthorhombic phase transition temperatures, T_C and T_O-T. It also induces a relaxor phase transition and weakens the ferroelectricity of the ceramics. The ceramics become ‘softened’, leading to improvements in d₃₃, k_p, k_t and ε_r and a decease in E_c, Q_m and N_p. The ceramics with x=0.075–0.15 become optimum, having d₃₃=127–151 pC/N, k_p=0.43–0.44, k_t=0.43–0.44, ε_r=541–712, tanδ=1.75–2.48% and T_C=378–329 °C. PACS 77.65.-j; 77.84.Dy; 77.84.-s     

Ordering of SiO<Subscript>x</Subscript>H<Subscript>y</Subscript>C<Subscript>z</Subscript> islands deposited by atmospheric pressure microwave plasma torch on Si(100) substrates patterned by nanoindentation

SiO _x H _y C _z nanometric layers are deposited from hexamethyldisiloxane by atmospheric pressure microwave plasma torch on Si(100) substrates submitted to temperatures varying on the range [0 °C; 120 °C]. Atomic force microscopy (AFM) characterizations of samples grown at intermediate substrate temperatures (~30 °C) demonstrate a layer-by-layer growth (Frank van der Merwe growth) leading to smooth flat and compact films while films deposited at lower and higher substrates temperatures show an island-like growth (Volmer-Weber growth) generating a high surface roughness. Concomitantly, a detailed infrared spectroscopy analysis of the growing films evidences structural modifications due to changes in the bond types, Si-O-Si conformation and stoichiometry correlated with scanning electron microscopy and AFM characterizations. Then, deposition conditions and specific microstructure are selected with the aim of generating 3-dimensional SiO _x H _y C _z nanostructure arrays on nanoindented Si (100) templates. The first results are discussed.     

Scaling and self-similarity in Pb<Subscript>1-x</Subscript>Fe<Subscript>x</Subscript>S nanoparticle films

This paper addresses the issues of scaling and self-similarity in typical nanoparticle films. The role played by microscopic processes contributing to growth on these issues is probed. While we perform this investigation for a specific system viz., Pb_1-xFe_xS nanoparticle films for clarity of the procedures, the analysis is general and can be applied to a variety of systems obtained using different deposition techniques.     

Photoactive lead ions in ferroelectric Pb<Subscript>5</Subscript>Ge<Subscript>3</Subscript>O<Subscript>11</Subscript> and paramagnetic resonance

The recharging of lead matrix ions upon exposure to light in pure, doped, and nonstoichiometric lead germanate crystals has been studied using electron paramagnetic resonance. It has been shown that the maximum concentration of metastable Pb³⁺ ions is achieved in crystals doped with chlorine, fluorine, titanium, and in samples with excess lead oxide. The annealing activation energy and the parameters of the superhyperfine interaction of Pb³⁺ paramagnetic centers have been determined.     

Effect of interdiffusion of In and Al atoms on excitonic states in In<Subscript>x</Subscript>Ga<Subscript>1−x</Subscript>As/Al<Subscript>y</Subscript>Ga<Subscript>1−y</Subscript>As quantum dots

The effect of interdiffusion of aluminum and indium atoms on the exciton emission energy and binding energy in In_xGa_1?xAs/Al_yGa_1?yAs quantum dots is studied. It is shown that the emission energy increases monotonically with increasing diffusion length, while the binding energy has a maximum.     

Magnetic properties of Pb<Subscript>2</Subscript>Fe<Subscript>2</Subscript>Ge<Subscript>2</Subscript>O<Subscript>9</Subscript> single crystals

Single crystals of Pb₂Fe₂Ge₂O₉ have been grown. They were subjected to X-ray diffraction, magnetic, neutron diffraction, Mössbauer and spin resonance studies. It has been established that Pb₂Fe₂Ge₂O₉ is a weak ferromagnet with a Néel temperature T _N = 46 K, and the exchange and spin-flop transition fields have been estimated. It has been demonstrated that the weak ferromagnetic moment is actually the result of the single-ion anisotropy axes for the magnetic moments of different magnetic sublattices being not collinear.     

Polarization processes in BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> and SrBi<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics in infralow-frequency fields

The dielectric nonlinearity in BaBi₂Nb₂O₉ and SrBi₂Ta₂O₉ layered ceramics was studied by measuring their polarization loops and reverse dependences of permittivity. It was shown that the features of the dielectric response of BaBi₂Nb₂O₉ and SrBi₂Ta₂O₉ in strong fields can be explained by glass-like properties and the contribution of the domain structure of the ferroelectric material to repolarization processes, respectively.     

Long-time relaxation phenomena in Pb<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>Sc<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> (PBSN-6) single crystals

Long-time polarization relaxation in the temperature range where PBSN-6 single crystals reside in the relaxor state was studied. An analysis of the time dependence of the permittivity ε′(t) performed at measuring frequencies from 1 Hz to 1 kHz in weak electric fields E₀ showed that the relaxation (or freezing) times derived by extrapolating relations of the type ε′(t) ～ log(t/t₀) and ε′(t) ～ exp{?[ln(t/t₀)]_β} range from 10⁸ to 10¹¹ min and depend substantially on the bias voltage applied to the sample. A study of the pattern of the dielectric response in moderate and strong infralow-frequency fields revealed that, after a sample was maintained under a bias lower than the coercive force, it no longer exhibited the additional anomalies in the amplitude dependences of the effective loss tangent tan_eff(E₀) than were observed in a thermally recuperated sample.     

Magnetic state of intercalation compounds in the Cr<Subscript>x</Subscript>TiTe<Subscript>2</Subscript> system

The temperature and field dependences of the magnetic characteristics of chromium-intercalated titanium ditelluride compounds are investigated over a wide range of chromium concentrations. The Cr_0.5TiTe₂ compound is studied by neutron diffraction. It is revealed that the system under investigation can occur in different magnetic states depending on the chromium concentration. An analysis of the experimental results demonstrates that the interaction between magnetic moments of chromium ions is predominantly ferromagnetic in character. An increase in the chromium concentration leads to ferromagnetic behavior with a pronounced magnetic hysteresis. The magnetic moments of chromium ions in these compounds are estimated.