Quadrupole interaction of tantalum impurities in bismuth metal

The time differential perturbed angular correlation technique has been used in the measurement of the electric quadrupole interaction of Ta impuritiy in bismuth metal. The interaction frequencies at 293, 400 and 500 K have been observed to be 288±1.5, 266.9±3 and 244.5±4.3 MHz respectively. The electric field gradient at 293 K is 4.75±0.3 × 10¹⁷ V/cm² with the temperature coefficientB=2.2±0.2 × 10⁻⁵ (K)^−3/2.     

Local ordered magnetic fields in bismuth dielectrics. 209Bi NQR in Bi4Ge3O12 single crystal

The results of the ²⁰⁹Bi NQR experiments carried out on α-Bi₂O₃, Bi₃O₄Br, Bi₂M₄O₉ (M=Al, Ga), Bi₂Ge₃O₉, and Bi₄Ge₃O₁₂ showed that these compounds are not diamagnets in the conventional sense. The Zeeman perturbed zero-field ²⁰⁹Bi NQR spectra gave an indication that local ordered magnetic fields of the order of 30–200 G exist in these substances comprising neither transition nor rare earth elements. Further aspects of this principally new phenomenon of yet unknown nature were studied by the ²⁰⁹Bi NQR experiments on the Bi₄Ge₃O₁₂ single crystal in external magnetic fields below 500 Oe, applied at various orientations with respect to the crystal axes. The spectral patterns of dramatically increased intensity and multiplicity, caused by the unknown magnetism of the compound, were observed in applied fields and modeled. Based on the results of the modeling, the conclusions were made that at least four magnetically non-equivalent Bi sites characterized by antiferromagnetically ordered local fields of the order of 30 G are present in the Bi₄Ge₃O₁₂ crystal; the intensity increase was interpreted to arise from the change in orientation of the electric field gradient axes at the Bi site upon applying an external magnetic field.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

Determination of the (Na) Sternheimer antishielding factor by Na NMR spectroscopy on sodium oxide chloride, Na3OCl

The (Na⁺) Sternheimer antishielding factor γ_∞ (Na⁺) was determined by ²³Na NMR spectroscopy on sodium oxide chloride, Na₃OCl. The quadrupolar coupling constant of the sodium ion in Na₃OCl was determined to QCC=11.34 MHz, which presents the largest coupling constant of a sodium nucleus observed so far. Applying a simple point charge model, the largest principal value of the electric field gradient at the sodium site was calculated to V_zz=−6.76762·10²⁰ V/m². From these values we calculated the (Na⁺) Sternheimer antishielding factor to γ_∞ (Na⁺)=−5.36. In sodium oxide, Na₂O, we observed an isotropic chemical shift of δ_CS=55.1 ppm, referenced to 1 M aqueous NaCl (δ=0 ppm).     

Anomalous magnetism and 209Bi nuclear spin relaxation in Bi4Ge3O12 crystals

The quadrupole ²⁰⁹Bi spin–spin and spin–lattice relaxation were studied within 4.2–300 K for pure and doped Bi₄Ge₃O₁₂ single crystals which exhibit, as was previously found, anomalous magnetic properties. The results revealed an unexpectedly strong influence of minor amounts of paramagnetic dopants (0.015–0.5 mol.%) on the relaxation processes. Various mechanisms (quadrupole, crystal electric field, electron spin fluctuations) govern the spin–lattice relaxation time T ₁ in pure and doped samples. Unlike T ₁, the spin–spin relaxation time T ₂ for pure and Nd-doped samples was weakly dependent on temperature within 4.2–300 K. Doping Bi₄Ge₃O₁₂ with paramagnetic atoms strongly elongated T ₂. The elongation, although not so strong, was also observed for pure and doped crystals under the influence of weak (～30 Oe) external magnetic fields. To confirm the conclusion about strong influence of crystal field effects on the temperature dependence of T ₁ in the temperature range 4.2–77 K, the magnetization vs. temperature and magnetic field was measured for Nd- and Gd-doped Bi₄Ge₃O₁₂ crystals using a SQUID magnetometer. The temperature behavior of magnetic susceptibility for the Nd-doped crystal was consistent with the presence of the crystal electric field effects. For the Gd-doped crystal, the Brillouin formula perfectly fitted the curve of magnetization vs. magnetic field, which pointed to the absence of the crystal electric field contribution into the spin–lattice relaxation process in this sample.     

Dielectric and structural relaxation phenomena in Na0.5Bi0.5TiO3 single crystal

Abstract

Dielectric permittivity studies of Na_0.5Bi_0.5TiO₃ single crystals in a broad range of frequency up to 10 MHz and temperature 300—823 K are reported. In this temperature range dielectric dispersion below 1 MHz has been found. The obtained data were fitted to the Cole-Cole relation. The mean relaxation time τ is strongly temperature dependent (0.04 ? 2.6 × 10^?5 s). A remarkable hysteresis effect in the values of τ on cooling and heating took place. The Δε(T) dependence (the maximal value of Δε ～ 400) is similar to the global ε′(T) response at low frequency. An isothermal structural transformation in Na_0.5Bi_0.5TiO₃ was observed by X-ray measurements. The order of the time in which the transformation takes place (～300 minutes) corresponds to the time in which the strongest time evolution of electric permittivity and time changes of dielectric dispersion were detected.     

Hyperfine Interactions of 12B in CaB6

The hyperfine interactions of short-lived β-emitter ¹²B implanted into a CaB₆ crystal have been studied by means of the β-NMR technique. An electric quadrupole splitting has been observed at room temperature from which an electric field gradient of q=−(1.34±0.05)×10²¹ V/m² was determined. From the present result, it was found that the ¹²B nuclei are mainly implanted in the substitutional boron site. This revised version was published online in September 2006 with corrections to the Cover Date.     

High order electron paramagnetic resonance transitions of Gd3+ in Pr2Zn3(NO3)12·24H2O single crystals

Electron paramagnetic resonance of Gd³⁺ in Pr₂Zn₃(NO₃)₁₂ · 24H₂O single crystals has been studied at ∼ 9.45 GHz and at 285 K. In addition to the allowed fine structure lines (ΔM=± 1) some weak low field lines identified as ΔM = ± 2 transitions have been observed.     

X-ray excited luminescence and photoluminescence of Bi4(GeO4)3 glass-ceramics

Bi₄(GeO₄)₃ glass materials have been characterized by X-ray excited luminescence, photoluminescence and cathodo-luminescence measurements. The materials were obtained by crystallization at different temperatures and their spectroscopic parameters were compared before and after crystallization. Thermoluminescence curves recorded after electron irradiation of BGO glass behave similarly to BGO crystals, showing several peaks between 408 K (135 °C) and 610 K (337 °C). The differences between the Bi₄(GeO₄)₃ crystals and glass materials are believed to result from the random distribution of GeO₄ tetrahedra around Bi³⁺ ions which influences the photoluminescence and TL parameters. The CL images of glass-ceramic samples obtained by partial crystallization at 600 °C show luminescent crystalline structures, which are probably responsible for the increase in scintillation efficiency.     

81Br NQR Study of [NH3(CH2) n NH3]CdBr4 (n = 4 and 5) and [NH3(CH2) n NH3]ZnBr4 (n = 5 and 6)

⁸¹Br NQR frequencies and differential scanning calorimetry (DSC) were measured as a function of temperature. [NH₃(CH₂)₄ NH₃]CdBr₄ (1) and [NH₃(CH₂)₅NH₃]CdBr₄ (2) showed a doublet and quartet ⁸¹Br NQR spectrum, respectively. [NH₃(CH₂)₅NH₃]ZnBr₄ (3) and [NH₃(CH₂)₆NH₃]ZnBr₄ (4) exhibited a four-line ⁸¹Br NQR spectrum. From the NQR results, it is inferred that (1) and (2) consist of infinite two-dimensional sheets of corner-sharing CdBr₆ octahedra, whereas (3) and (4) have isolated [ZnBr₄]²⁻ tetrahedra. All of the crystals except (1) showed at least one structural phase transition above 380 K.     

Quadrupole moment of the doubly closed shell +1 nucleon nucleus41Sc(Iπ=7/2−)

The nuclear electric quadrupole moment of⁴¹Sc(I^π=7/2⁻) was experimentally determined by use of the NMR detection in which the asymmetric β-ray distribution from spin polarized nuclei was monitored. The magnetic interaction of the state with high external magnetic field and the nuclear quadrupole interaction with the electric field gradient obtained in TiO₂ crystal were studied. The field gradient seen to the implanted⁴¹Sc was measured independently by the high field NMR detection on the stable isotope⁴⁵Sc located in the equivalent⁴¹Sc site with. |Q(⁴¹Sc;I^π=7/2⁻)|=(0.120±0.006) b was determined.     

Theψ-particles in an SU4 scheme with anomalous currents

The recently discovered narrow peaks (theψ-particles) in e⁺e⁻ system at 3.105 and 3.695 GeV are interpreted as hadrons in a broken SU₄ symmetry scheme. A new additional additive quantum number, parachargeZ, is combined with the usual SU₃ quantum numbers in the group SU₄. Theψ (3.1) is assigned to a near ideally mixed15⊕1 multiplet of vector mesons (containing theρ) as theI=Y=0, charge conjugationC=−combination ofZ=±1.members. Theψ (3.7) is assigned correspondingly to another mixed15⊕1 multiplet containing theρ′ (1600). The hadronic electromagnetic interactions are modified by the addition of (non-minimal) anomalous pieces that can changeZ. The decays of theψ-particles are discussed. New enlarged SU₄ multiplets of other hadrons are proposed. Tests of our scheme are put forward. The most crucial test will be the observation of two rather broad resonances in e⁺ e⁻ collisions with masses around 4.2 GeV and 5.1 GeV. Another prediction is the presence of energetic photons in the decays of theψ-particles. Important results concerning the recently observed phenomena in the process e⁺e⁻→hadrons follow in this scheme.     

Incommensurate phase in the layered hexagonal crystal Cs3Bi2I9

An incommensurate phase is observed in a Cs₃Bi₂I₉ crystal, which belongs to the family of layered A₃B₂X₉ structures. Data from ¹²⁷I NQR and x-ray powder diffraction patterns show that the second-order normal phase—incommensurate phase transition at T _i=220 K is accompanied by a P6₃/mmc↔P2₁/m symmetry change and takes place at the center of the Brillouin zone. The nature of the instability leading to the appearance of this little-studied form of incommensurability is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1105–1108 (June 1997)     

Synthesis and photoluminescence properties of MZr2(PO4)3:Eu3+; Bi3+ (M=Na; K) phosphors

A series of new red phosphors, MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K), were synthesized using the solidstate reaction method, and their photoluminescence spectra were measured. The MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors were efficiently excited by an ultraviolet (UV; 395 nm) source, and showed intense orange-red emission at 595 nm. Further investigation of the concentration-dependent emission spectra indicated that the MZr₂(PO₄)₃:Eu³⁺; Bi³⁺ (M=Na; K) phosphors exhibit the strongest luminescence intensity when y = 0.01 in NaZr_2(0:95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ and y = 0.09 in NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺, whereas the relative PL intensity decreases with increasing Bi³⁺ concentration due to concentration quenching. The addition of Bi³⁺ widens the excitation band of NaZr_2(0.95−y)(PO₄)₃:Eu_0.10³⁺, Bi_2y ³⁺ around 320 nm, which provides the useful idea of broadening the excitation band around 300–350 nm to fit the ultraviolet chip.     

Sol-gel法制备Bi0.85Nd0.15FeO3多铁性薄膜

利用sol-gel法在Pt/Ti/SiO₂/Si衬底上制备出Bi_0.85Nd_0.15FeO₃薄膜.研究退火温度对其晶相形成的影响,发现在450 ℃退火时,Bi_0.85Nd_0.15FeO₃晶相开始形成,但是结晶较差,而且存在杂相;在500—600 ℃退火可以获得单相Bi_0.85Nd_0.15FeO₃薄膜,退火温度升高有利于其结晶.对600 ℃退火的Bi_0.85Nd_0.15FeO₃薄膜的介电、铁电和电磁性能进行了测试.在测试频率为1 MHz时,其介电常数和介电损耗分别为145,0.032;饱和磁化强度大约为44.8 emu/cm³;剩余极化值(2P_r)大约是16.6 μC/cm². 关键词： sol-gel法 0.85Nd_0.15FeO₃薄膜')" href="#">Bi_0.85Nd_0.15FeO₃薄膜 铁电性能 铁磁性能     

The microwave spectrum of 4-pyridine carbaldehyde (isonicotinealdehyde)

The microwave spectrum of 4-pyridine carbaldehyde has been investigated in the region 8 to 40 GHz. Rotational transitions have been observed and assigned for the ground state and two excited states of the torsion mode. Analysis yields precise rotational constants (A = 5519.04 ± 0.08, B = 1559.17 ± 0.03, C = 1216.11 ± 0.02 MHz) which prove the molecule to be planar. Centrifugal distortion constants have also been obtained. Analysis of the observed ¹⁴N quadrupole fine structure yields the following quadrupole coupling constants (in MHz): χ_aa = ?4.67 ± 0.09; χ_bb = 1.19 ± 0.26; χ_cc = 3.48 ± 0.26. The electric field gradient about the nitrogen nucleus is thus similar to that of pyridine.     

Electromechanical and ferroelectric properties of (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3- (Bi1/2Li1/2)TiO3-BaTiO3 lead-free piezoelectric ceramics for accelerometer application

Lead-free (0.90-x)(Bi_1/2Na_1/2)TiO₃-0.05(Bi_1/2K_1/2)TiO₃-x(Bi_1/2Li_1/2)TiO₃-0.05BaTiO₃ piezoelectric ceramics (abbreviated as BNKLBT-100x, with x ranged from 0 to 2.5 mol %) were prepared by a conventional mixed oxide method. Effects of the amount of (Bi_1/2Li_1/2)TiO₃ (BLT) on the electrical properties and crystal structure of the BNKLBT ceramics were examined. BNKLBT-1.5 ceramics have good properties with piezoelectric constant d₃₃=163 pC/N, electromechanical coupling factor k_p=0.33, k_t=0.53, relative permittivity ε_r=785 and dissipation factor cosδ=2.2% at 1 kHz. The sample has larger remnant polarization than BNKLBT-0 ceramics and the same coercive field as BNKLBT-0 ceramics. X-ray diffraction analysis shows that the incorporated BLT diffuses into the BNT–BKT–BT lattice to form a solid solution during sintering, but changes the crystal structure from rhombohedral to tetragonal symmetry at higher BLT amounts. Depolarization temperature (T_d) of the BNKLBT-100x ceramics increases from 102 °C to ∼136 °C for BNKLBT-0 to BNKLBT-2.5. BNKLBT-1.5 is used as the transduction element in compressive type accelerometer and its sensitivity is calibrated by the back-to back method. Within the ±2.5% tolerance, the lead-free accelerometer has a mean value of 2.97 pC/ms^-2 within 50 Hz–12.45 kHz and the lead-based accelerometer has a mean value of 4.34 pC/ms^-2 within 50 Hz to 8.24 kHz. PACS 77.22.Ej; 77.84.-s; 85.50.-n     

A novel red-emitting phosphor Ca9Bi(PO4)7:Eu3+ for near ultraviolet white light-emitting diodes

Red phosphors Ca₉Bi_1-x(PO₄)₇:xEu³⁺ (x = 0.06, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80 and 1.00) were synthesized by a conventional solid-state reaction (SSR) route. The X-ray diffraction patterns, photoluminescence spectra, ultraviolet–visible reflection spectroscopy, decay time and the International Commission on Illumination (CIE) chromaticity coordinates of these compounds were characterized and analyzed. The Eu-doped Ca₉Bi(PO₄)₇ phosphors exhibited strong red luminescence which peaks located at 615 nm due to the ⁵D₀→⁷F₂ electric dipole transition of Eu³⁺ ions after excitation at 393 nm. Ultraviolet–visible spectra indicated that the band-gap of Ca₉Bi_0.30(PO₄)₇:0.70Eu³⁺ is larger than that of Ca₉Bi(PO₄)₇. The results indicate that the phosphor Ca₉Bi_0.30(PO₄)₇:0.70Eu³⁺ can be a suitable red-emitting phosphor candidate for LEDs.     

Electric quadrupole interaction of210Po(6+) in Bi single crystal

The electric quadrupole coupling constant of the²¹⁰Po(6⁺) isomer in a Bi single crystal was measured as a function of the temperature using the time-differential perturbed angular correlations technique. The electric field gradient (EFG) for Po in Bi is found to be temperature independent in the range 77–477 K. Using a calculated value of the nuclear quadrupole moment, the magnitude of the EFG is derived, and in turn serves to re-examine the systematics of quadrupole moments of λh ₉ ^2/2 configurations in the lead region.     

Adjoint representation admixture to weak nonleptonic decays in SU(4) and SU(8)

In order to remove some of the unsatisfactory features of the GIM model, we consider15-admixture in SU(4). ΔC=±ΔS decays remain unaffected. Lee-Sugawara sum-rule is obtained.15-admixture is extended then to63-admixture in SU(8). The most general Hamiltonian (H _w∼63⊕720⊕1232) in SU(8) is found to give Lee-Sugawara relation and Σ₊ ⁺=0 forS-wave decays of uncharmed baryons. Decay amplitude relations for ΔC=−1, ΔS=0 mode are obtained.