Ferroelastic phase transition and anomalous elastic and thermal properties of betaine borate (CH3)3NCH2COO·H3BO3

The temperature and pressure derivatives of the elastic constants of orthorhombic betaine borate, (CH₃)₃NCH₂COO·H₃BO₃, have been determined by measuring temperature and stress induced shifts of resonance frequencies of thick plates at ca. 15 MHz in the range between 140 and 300 K and 0 and 3 kbar. The elastic ‘shear’ resistance c₄₄ exhibits a value as low as 0.0492×10¹⁰Nm^-2at 293 K. With decreasing temperature c₄₄ approaches zero at ca. 142.5 K, indicating an acoustic soft mode behaviour connected with a ferroelastic phase transition. The softening of c₄₄ is described in a good approximation by c₄₄(T)_p=0 =alogT/T₀ with a=0.0663×10¹⁰Nm^-2 and T₀ = 139.5 K. Further, c₄₄ decreases with increasing pressure according to the linear relation c₄₄(p)_{T=293 K} = 0.0492?0.184×10^-4p (p in bar, c₄₄ in 10¹⁰ Nm^-2). All other elastic constants show a quite normal temperature and pressure dependence. At 293 K the transition is induced by a pressure of 2.65 kbar. The transition temperature T_c depends linearly on pressure according to T_c = 142.5+0.0568 p (pinbar, T_cinK). Passing through the transition no discontinuous change of the lattice constants is observed. The three principal coefficients of thermal expansion and the pressure derivatives of the dielectric constants exhibit discontinuities at the transition. The transition is of strongly second order.     

Impedance and dielectric studies of ferroelectric SrBi2Nb2O9 ceramics

This paper reports the dielectric and impedance characteristics of ferroelectric SrBi₂Nb₂O₉ (SBN) ceramics in the 100 Hz-1 MHz frequency range at various temperatures (300-823 K). A strong low frequency dielectric dispersion (LFDD) associated with an impedance relaxation has been found to exist in these ceramics in the temperature range 573-823 K. The Z″ of the AC complex impedance showed two distinct slopes in the frequency range 100 Hz-1 MHz suggesting the existence of two dispersion mechanisms. This non-ideal behavior has been explained on the basis of the expression, Z*=R₀/(1+(iω/ω₁)^m+(iω/ω₂)ⁿ) [J. Phys. Chem. Solids 53 (1992) 1] where ω₁ and ω₂ characterize the lattice response and the charge carrier behavior, respectively. The exponents m and n were obtained from the curve fitting. The exponent n was found to exhibit a minimum at the Curie temperature, T_c (723 K) whereas the m was temperature independent.     

Infrared study of lattice and free carrier effects in p-type CuInTe2 single crystals

Infrared reflectivity spectra of p-type CuInTe₂ single crystals were measured at room temperature for the polarization direction E ⊥ c and E | c in the wavenumber range from 55 to 4000 cm^?1. Fits to a dielectric function including contributions from lattice oscillators and free carriers gave the first determination of the effective hole masses of $\text{m}{}_{\mathrm{p\perp }}\text{m}{}_0\text{= 0.85}$ and $\text{m}{}_{\mathrm{p|}}\text{m}{}_0\text{= 0.66}$. Two optical phonon modes were found for both polarization directions.     

Experimental study of the final state interactions in the decays of 4ΛH → π−p3H amd 4ΛHe → π−p3He

Experimental results concerning the decay modes _Λ⁴H → π^?p³H and _Λ⁴He → π^?p³He are presented. A sample of _Λ⁴He → π^?p³He decays almost free from a contamination of other hypernuclear decay modes was selected. Some experimental distributions are compared with theoretical predictions.     

Synthesis and physical properties of antiperovskite-type compound In0.95CNi3

The compound In_0.95CNi₃ has been synthesized and the basic properties have been investigated. It has the typical antiperovskite structure (space group Pm3m, lattice parameter 3.7836 Å). The electronic specific coefficient γ and Debye temperature Θ_D are found to be 14.1 mJ/mol K² and 372 K, respectively. It behaves as a ferromagnetic metal below the Curie temperature (577 K). The emergence of ferromagnetism is suggested to originate from the deviation of the Ni/In atomic ratio from the ideal stoichiometry. The possible mechanisms have been discussed in detail in terms of this deviation.     

The magnetic field dependence of the structural transition temperature in La3S4 and La3Se4

The magnetic field dependence of the structural transition temperature T_m from the cubic to the tetragonal phase has been determined for single crystals of La₃S₄ and La₃Se₄. The observed field dependence of T_m can be accounted for by the band Jahn-Teller model of the coupling of an e_g-band to the shear mode of the cubic lattice without invoking any coupling to acoustic or optical phonons.     

Tunable diode laser measurements of N2- and air-broadened halfwidths: Lines in the (ν4 + ν5)0 band of 12C2H2 near 7.4 μm

Nitrogen- and air-broadened Lorentz halfwidths have been determined for 29 lines in the P and R branches of the (ν₄ + ν₅)⁰ combination band of ¹²C₂H₂ using a tunable diode laser spectrometer. Two tunable diode lasers operating in the region 1250–1380 cm^?1 were used in recording the data. For nitrogen broadening, the measured halfwidths at 296 K decrease from about 0.11 cm^?1 atm^?1 at |m| = 1 to about 0.05 cm^?1 atm^?1 at |m| = 30, where m = J″ + 1 for R-branch lines, m = ?J″ for P-branch lines, and J″ is the lower state rotational quantum number. On the average, the air-broadened halfwidths are 97% of the N₂-broadened halfwidths.     

A light neutral intermediate vector boson without large e+e−→ μ+μ− asymmetries

An effective SU(2)×U(1)×U(1)' electroweak theory is shown to permit the occurence of a pair of neutral intermediate vector bosons with masses 40 GeV?m_light?70 GeV, m^W.S._Z⁰<m_heavy?100 GeV. Neutrino neutral current interactions are shown to be the same as in the standard electroweak model, and e⁺e^?→μ⁺μ^? forward-backward asymmetries are within experimental bounds for m_light?40 GeV.     

Properties suggesting H3+-type clusters in some metallic hydrides

The p-c-T relationships for the hydrogen-rich phase of some metallic hydrides are calculated supposing the formation of H₃⁺ -type clusters in the metal lattice in equilibrium with the hydrogen gas. The experimental data for the hydride phase of LaNi₅, Pd, Nb (H?Nb? 0.75) and U are consistent with this model. Other properties reported in literature which seem to support this model are discussed.     

Luminescence and chromaticity of alkaline earth aluminate MxSr1−xAl2O4:Eu (M: Ca,Ba)

In order to prepare fluorescent material for UV-LED used as illumination light source, two series of Eu²⁺ doped (1 mol%) alkaline earth aluminate phosphors Ca_xSr_1−xAl₂O₄ and Ba_xSr_1−xAl₂O₄ were prepared. The crystal structure, relative quantum efficiency(Qr), peak wavelength(λ_p), color tuning and chromaticity were investigated by XRD patterns and photoluminescence (PL) on samples prepared by solid solution system (s series) and powder mixing system (m series) respectively. For the s series, the synthesized Ca_xSr_1−xAl₂O₄:Eu²⁺ powders show that the structure transforms from monoclinic to hexagonal at x?0.5, and λ_p increases from 442.3 to 529.7 nm with decreasing x. For the Ba_xSr_1−xAl₂O₄:Eu²⁺ system, the structure transforms from monoclinic to hexagonal at x?0.3, and λ_p decreases from 520.5 to 502.2 nm continuously from x=0 to 1. The shift in λ_p could be explained by the crystal field effect, which is affected by different coulomb attractive forces due to the various fraction of alkaline earth cation in the host lattice. Different phosphor properties prepared by either solid solution or powder mixing methods were characterized by chromaticity measurements for both reflective and transmissive modes.     

IR absorption in p-type pb0.97Sn0.03Se

IR absorption in p-type melt grown Pb_0.97Sn_0.03Se crystals is reported. The results for the room temperature absorption coefficient (α) in the wavelength region 2–15 μm are analysed. The indirect absorption edge is found to be at 0.26 eV for this ternary alloy. In the longwavelength region α is found to be proportional to λ², in agreement with the classical free carrier absorption expression. The conductivity effective mass of holes is found to be 0.067 m₀ at 300°K.     

Radiative corrections to νμ + N → μ− + X and their effect on the determination of ϱ2 and sin2θW

We study the O(α) corrections to σ_T(ν_μ + N → μ^? + X). The coefficient of the leading O(αln m_Z) contribution is given by a general theorem as in the case of β decay, while the energy scale accompanying m_Z in the argument of the logarithm as well as mass singularities and non-logarithmic terms are obtained by a detailed quark-parton model calculation. The effect of muon mass singularities, when there is an experimental vut in the low range of the y distribution, is also investigated. Combining these new results with our previous analysis of σ_T(ν_μ + N → ν_μ + X), we calculate theSU(2)_L × U(1) parameter ?_(νμ;h)² and evaluate the effect of the O(α) corrections on the determination of sin²θ_W^exp from deep inelastic ν_μ scattering. Applying these corrections to existing data, we obtain the weigthed average sin²θ_W^exp = 0.216 ± 0.010 ± 0.004. This value when used in conjuction with our previous analysis of the W^± and Z⁰ masses provides the predictions m_W = 83.0_?2.8^+3.0 GeV and m_Z = 93.8_?2.4^+2.5 GeV. For the weak interaction angle defined by modified minimal subtraction we find sin²θ_W(m_W) = 0.215 ± 0.010 ± 0.004, which is in very good agreement with the SU(5) prediction we have recently given.     

Low temperature electrical conductivity and magnetoconductivity of Fe39Ni39Mo4Si6B12 and Co58Ni10Fe5Si11B16 metallic glass alloys

A detailed study on the weak localization phenomenon vis-a-vis electron-electron interaction effects in magnetic metallic glasses has been carried out. We measured the electrical conductivity and magnetoconductivity within the temperature range 1.8≤T≤300K. A maximum on the conductivity versus temperature curve exists atT=T _m. The conductivity was observed to follow aT ^1/2 law forT<T _m andT ² law forT>T _m. Magnetoconductivity data of these alloys indicate the prominence of electron-electron interaction at low temperatures. The authors have determined the inelastic scattering field and spin-orbit scattering field from the magnetoconductivity data. The inelastic scattering field obeys aT ^p law (p=2) at low temperatures.     

Study on vacancy motion in Y2O3-doped CeO2 by 17O NMR technique

The ¹⁷O NMR measurement was made to elucidate the microscopic nature of vacancy motion in Y₂O₃-doped CeO₂. Spin-lattice relaxation rate, T^?1₁, spin-spin relaxation rate, T^?1₂, and resonance intensity were measured at v₀ = 8.13 MHz as a function of temperature [385 < T (K) < 1110] and composition [$\text{0.06 <}\text{Y}{}_2\text{O}{}_3\text{(}\text{m}\text{o}\text{) < 6}$]. The static electric field gradient associated with lattice defects resulted in the composition dependences of the line width and the intensity. In low dopant concentrations, doubly peaked temperature dependence of T^?1₁ was found, while a single and asymmetric peak was observed in high concentrations. T^?1₁ of 4.0 and 6.0 $\text{m}\text{o}$ doped samples were analyzed using a barrier height distribution model for the oxygen vacancy jump. The mean value of the activation energy was found to increase with the Y₂O₃ concentration.     

Investigation of magnetocaloric effect in La0.45Pr0.25Ca0.3MnO3 by magnetic,differential scanning calorimetry and thermal analysis

We investigated magnetocaloric effect in La_0.45Pr_0.25Ca_0.3MnO₃ by direct methods (changes in temperature and latent heat) and indirect method (magnetization isotherms). This compound undergoes a first-order paramagnetic to ferromagnetic transition with T_C=200 K upon cooling. The paramagnetic phase becomes unstable and it transforms into a ferromagnetic phase under the application of magnetic field, which results in a field-induced metamagnetic transition (FIMMT). The FIMMT is accompanied by release of latent heat and temperature of the sample as evidenced from differential scanning calorimetry and thermal analysis experiments. A large magnetic entropy change of ΔS_m=−7.2 J kg⁻¹ K⁻¹ at T=212.5 K and refrigeration capacity of 228 J kg⁻¹ are found for a field change of ΔH=5 T. It is suggested that destruction of magnetic polarons and growth of ferromagnetic phase accompanied by a lattice volume change with increasing magnetic field is responsible for the large magnetocaloric effect in this compound.     

Optical,thermal and polaron energy levels in α-Al2O3

Calculations of the thermal band gap, ionisation energy and O(2p) valence band width are reported based on defect lattice methods. From these it is estimated that the large polaron is the preferred hole state in α-Al₂O₃ by about 0.4 eV. Theoretical values for the optical and thermal energy levels of Ti³⁺ in α-Al₂O₃ are also reported.     

Diode laser spectroscopy of the ν6 band of 13CH3l and the ν″6 band of 12CH2Dl

The ν₆ band of ¹³CH₃I and the ν″₆ band of ¹²CH₂DI have been recorded under Doppler-limited resolution in the region 820–866 cm^?1 using a tunable diode laser spectrometer. For ¹³CH₃I the constants for the ν₆ band were determined by simultaneous analysis of seven ^pQ(J,K) branches and several ^pP(J,K) and ^pR(J,K) transitions. For ¹²CH₂DI, the slight asymmetry introduced by the single D atom gives rise to noticeable asymmetry effects in the spectra of some of the ^pQ(J,K) subbands. From the analysis of six such subbands, the molecular constants for the ν″₆ level were determined.     

Influence of pH on characteristics of BaFe12O19 powder prepared by sol–gel auto-combustion

BaFe₁₂O₁₉ powders with nanocrystalline sizes were produced by sol–gel auto-combustion. Fe³⁺ and Ba²⁺, in a molar ratio of 11.5, were chelated by citric acid ions at different pH. After dehydration, auto-combustion and calcinations, BaFe₁₂O₁₉ powders were formed. TG/DSC indicated the action to form BaFe₁₂O₁₉ first occurred at about 800. XRD patterns of the annealed powders showed that the well-crystalline powder was produced when pH=10. In addition, the data from XRD showed the lattice parameters a and c, and the unit-cell volume V had a little decrease and the density went up with the increasing pH. The data from PPMS exhibited that pH in the starting solution had an important influence on magnetic properties. In this case, BaFe₁₂O₁₉ powder, of maximum magnetization M(3 T)≈60 A m²/kg, the remanent magnetization M_r≈33 A m²/kg and the intrinsic coercive H_c≈432 kA/m, was produced under the molar ratio of citric acid to the metal nitrate of 1.5 when pH=10.     

Optical absorption, fluorescence and decay properties of Pr-doped PbO-H3BO3-TiO2-AlF3 glasses

Spectroscopic and laser properties of PbO-H₃BO₃-TiO₂-AlF₃ glasses doped with 0.1, 0.5, 1.0 and 2.0 mol% of Pr₆O₁₁ have been studied. Optical absorption spectra were recorded in the UV-vis-NIR regions and the observed absorption bands were assigned to different electronic transitions from ³H₄ ground state of 4f² configuration. The three phenomenological Judd-Ofelt (J-O) parameters Ω_t (t=2, 4, 6) were determined from the measured oscillator strengths by including as well as excluding the ³H₄→³P₂ hypersensitive transition in J-O analysis. The emission characteristics such as stimulated emission cross-sections (σ_e), measured branching ratios (β_m), measured lifetimes (τ_m), quantum efficiencies (η) and gain parameters (σ_e×τ_m) have been evaluated for the principal intermanifold transitions of Pr³⁺ from the ³P₀ and ¹D₂ states to the lower lying manifolds in the visible region. From the emission and decay measurements, the effect of Pr³⁺ ion concentration on the quenching of the ¹D₂ measured lifetimes has been discussed.     

Hyperfine interactions in some Aurivillius Bim+1Ti3Fem−3O3m+3 compounds

X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods to investigate the structure and hyperfine interactions in the series of Bi_m+1Ti₃Fe_m−3O_3m+3 Aurivillius compounds with m=4, 6, 7 and 8. Samples were synthesized by the solid-state sintering method at various temperatures. As X-ray diffraction analysis proved, the compounds formed single phases at temperature above 993 K. Mössbauer studies have confirmed diffraction measurements. Compounds synthesized at 993 K contained residual hematite, however these sintered at elevated temperatures were single-phased materials. Room-temperature Mössbauer spectra of Bi_m+1Ti₃Fe_m−3O_3m+3 compounds revealed their paramagnetic properties, what is consistent with the literature data concerning the Néel temperature of these ceramics (T_N is smaller than room temperature). Detailed analysis of MS spectra allowed to state that iron ions may occupy both tetrahedral and octahedral sites in the crystallographic lattice of Aurivillius compounds.