Quadrupole interactions in lithium borodeuteride

Polycrystalline samples of lithium borohydride and borodeuteride, LiBH₄ and LiBD₄, are studied by ²H, ⁷Li, and ^10,11B NMR in 7.04 T and 9.35 T magnetic fields in the temperature range 116–580 K. The ^10,11B NMR line shape of the orthorhombic phase of LiBH₄ and LiBD₄ suggests that first-order quadrupole interaction takes place. The quadrupole coupling constant (QCC) χ _q and asymmetry parameter η of the electric field gradient tensor for ¹¹B are described by linear temperature dependences: χ _q (¹¹B) = 177 ? 0.24T and η = 0.043 + 0.0014T. The electric field gradient at the positions of boron nuclei is created by external charges, primarily lithium cations. In the range of 388–391 K, the ⁷Li NMR line shape reflects the coexistence of two phase modifications of LiBH₄ and LiBD₄ and the occurrence of a reversible first-order phase transition. In the temperature range of 390–530 K, the ⁷Li NMR line shape represents a first-order quadrupole perturbed spectrum with zero asymmetry parameter and a weakly temperature dependent ⁷Li QCC. The spin-lattice relaxation time and the NMR line shape of ²H are interpreted in terms of the reorientation of the BD ₄ ^? anion about their proper symmetry axes C₂ and C₃.     

Local structure analysis of smoky and colorless topaz using single crystal Al NMR

The angular dependence of the ²⁷Al NMR spectrum was measured for single crystals of smoky and colorless topaz, Al₂SiO₄(F,OH)₂. Smoky topaz was obtained by irradiating high energy neutrons to colorless topaz. The quadrupole coupling constant e²Qq/h and the asymmetry parameter η were obtained from the analysis of the angular dependences of quadrupole splitting of the ²⁷Al NMR spectrum. The local structures around the aluminum atoms in smoky and colorless topaz were discussed from the magnitude and the direction of the electric field gradient. The directions of principal axes of the EFG tensor of ²⁷Al were close to the directions of Al-O and Al-F bonds. The difference in the bond lengths between Al(1)-F(1) and Al(1)-F(2) was found to affect the x and y components of the EFG tensor.     

Ga and Pt NMR study of UPtGa5

^69,71Ga and ¹⁹⁵Pt NMR/NQR measurements have been carried out for the 5f-antiferromagnet, UPtGa₅. From a NMR study using a single crystal sample, Knight shift measurements are reported for two different Ga sites and for Pt. The principal axes of the electrical field gradient tensor at both Ga sites have been determined and the values of the splitting parameter ν_Q and the asymmetry parameter η have been evaluated. The hyperfine coupling constants with the external field along various directions are also reported for the two Ga sites and Pt.     

NMR spin echoes and quadrupole effects in nickel single crystals

NMR spin echo measurements of naturally abundant⁶¹Ni have been performed with Néel-type nickel single crystals at 4.2 K. The NMR excitation condition could properly be chosen in order to get signals either from nuclei situated within magnetic domains or within domain walls. In both cases a quadrupole splitting of the NMR line could be observed. By applying an external magnetic field, the direction of the domain magnetization could be varied with respect to the fcc crystal lattice. From the variation of the quadrupole splitting with the crystallographic direction, the tensor of the electric field gradient (EFG) has been derived. The quadrupole splittings and the corresponding field gradients in the principal axis system of the EFG are: Δv_Q kHz, Δv_Q kHz, Δv_Q kHz, V_<111>=(6.6±0.5)·10¹⁸ V/m², V_<110>=4.6±0.5)·10¹⁸ V/m², V_<112>=(2.0±0.5)·10¹⁸ V/m².     

2H NMR of Deuterofullerites C60D x

Deuterofullerites C₆₀D _x have been studied by means of ²H NMR spectroscopy. It has been established that there are two types of carbon–deuterium bindings in the samples under study: tip C–D with quadrupole constant coupling (QCC) 171 kHz and bridge –C...D...C– with QCC 56 kHz. It is possible that the latter bond is a result of the rigidity of the lattice, which is unusual for fullerene compounds.     

NMR study of the electric field gradient in the paramagnetic phase of M<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> (M = Co,Ni) compounds

The NMR spectra and the decay of a spin echo signal from ⁵¹V nuclei in Kagome-staircase Co₃V₂O₈ (CVO) and Ni₃V₂O₈ (NVO) single crystals are measured in the temperature range 30–300 K and a magnetic field H ₀ = 20 kOe. The orientation dependences of the ⁵¹V NMR line shape are used to determine the electric field gradient (EFG) parameters, namely, quadrupole frequency ν _Q and asymmetry parameter η. These parameters for NVO and CVO are ν _Q = 180(10) kHz, η = 0.5(1) and ν _Q = 130(10) kHz, η = 0.6(1), respectively. A comparison of the results of calculating EFG tensors with a point charge model and the NMR data indicates that the crystallographically equivalent vanadium atoms in the Ni₃V₂O₈ and Co₃V₂O₈ compounds differ in the EFG axis orientation. M₃V₂O₈ crystals are found to have vanadium positions (V1, V2) with different orientations of the z axis, which specifies the direction of the principal value of EFG (V _zz ): these orientations lie in the bc plane and make an angle of either +51(5)° (V1) or −51(5)° (V2) with axis c. In the temperature range 30–300 K, the EFG tensor components and the local symmetry of the charge surrounding of the vanadium positions in NVO and CVO oxides are found to change insignificantly.     

LiKSO4低温相变的核磁共振研究

研究了LiKSO₄中⁷Li的核磁共振谱与温度及晶体取向的关系。证实了在T_c=195K存在一个结构相变,并由实验数据推导出在这一温度以下,晶体的对称性低于P31c,每单胞至少含有六个分子式。没有证据说明有一个无公约相存在。测得181K的四极耦合常数为38.9kHz,不对称因子η=0.46,电场梯度主轴方向z与原c轴成11.6°角。 关键词：     

Study of nuclear quadrupole interactions and quadrupole Raman processes of Ga and Ga in a β-Ga2O3:Cr single crystal

Nuclear magnetic resonance (NMR) data and the spin–lattice relaxation times, T₁, of ⁶⁹Ga and ⁷¹Ga nuclei in a β-Ga₂O₃:Cr³⁺ single crystal were obtained using FT NMR spectrometry. Four sets of NMR spectra for ⁶⁹Ga (I = 3/2) and ⁷¹Ga (I = 3/2) were obtained in the crystallographic planes. The ⁶⁹Ga and ⁷¹Ga nuclei each had two chemically inequivalent Ga_I and Ga_II centers. Each of the ⁶⁹Ga and ⁷¹Ga isotopes yielded two different central NMR resonance lines originating from Ga_I and Ga_II sites. The nuclear quadrupole coupling constants and asymmetry parameters of ⁶⁹Ga_I, ⁶⁹Ga_II, ⁷¹Ga_I, and ⁷¹Ga_II centers in a β-Ga₂O₃:Cr³⁺ crystal were obtained. Analysis of the EFG tensor principal axes (PAs) for Ga nuclei and the ZFS tensor PAs for the Cr³⁺ ion confirmed that the Cr³⁺ paramagnetic impurity ion substitutes for the Ga³⁺ ion in the oxygen octahedron. In addition, the temperature dependencies of the ⁶⁹Ga and ⁷¹Ga relaxation rates were consistent with Raman processes, as T₁⁻¹ ∝ T². Even though the Cr³⁺ impurities are paramagnetic, the relaxations were dominated by electric quadrupole interactions of the nuclear spins in the temperature range investigated.     

The local structure of Cs(I) and Cs(II) in a Cs2ZnCl4 single crystal studied by nuclear magnetic resonance

The rotation patterns of the ¹³³Cs (I=7/2) nuclear magnetic resonance (NMR) in a Cs₂ZnCl₄ single crystal grown by using the slow evaporation method were measured in two mutually perpendicular crystal planes. Two different groups of Cs resonances were recorded; this result points to the existence of two types of crystallographically inequivalent Cs(I) and Cs(II). The angular dependences of the NMR spectra led to different values for the quadrupole coupling constants and asymmetry parameters: e²qQ/h=148 kHz and η=0.11 for the Cs(I) ion, and e²qQ/h=274 kHz and η=0.66 for the Cs(II) ion. The EFG tensors of Cs(I) and Cs(II) are asymmetric, and the orientations of the principal axes of the EFG tensors do not coincide. Only, the principal Y-axes of the EFG tensors coincide for the Cs(I) and Cs(II) sites. The Cs(I) ion is surrounded by 11 chlorine ions, making it rather free and high in symmetry. The Cs(II) ion has only nine neighbors and seems to be more tight than the Cs(I) ion.     

Mössbauer effect study of SrEu2Fe2O7

The antiferromagnetic ferrite SrEu₂Fe₂O₇ was studied by Mössbauer effect of⁵⁷Fe in the range 77–650 K. Analysis of the data gives a Neel temperature of 544 K±2 K and an extrapolated effective magnetic fieldH(OK) of 545 kG. Good fit to the spectrum at 290 K is obtained withH _eff=475 kG, δ=0.37 mm/s, 1/2e ² qQ(1+η ²/3)=0.70mm/s, θ and ?=90°. The Brillouin function forS=5/2 poorly fits the experimental data of hyperfine magnetic fields. In the critical rangeH _eff can be described byH(T)=H(0)D(1?T/T _N )^β, where β nearly 0.29. The quadrupole interaction parameter is quite temperature independent, of the order of 0.69 mm/s in the paramagnetic state. Agreement with the value obtained by a point charge calculation is good. The largest axis of the EFG tensor,V _zz , lies in the plane (110), making an angle of 22.6° with thec axis. The direction of magnetization is nearly perpendicular toV _zz in [110] direction.     

Hyperfine and magnetic properties of 19e− (electron reservoir) sandwiches of Fe(I), C5R5FeC6R6 (where R=H or CH3) and (C6(CH3)6)2Fe+: Mössbauer experiments and molecular orbital calculations

The four compounds C₅H₅FeC₆H₆, C₅H₅Fe(CH₃₎₆, C₅(CH₃₎₅FeC₆(CH₃₎₆ and (C₆(CH₃₎₆₎₂Fe⁺ were studied by Mössbauer spectroscopy on powders. On the basis of semi-empirical molecular orbital calculation (Iterative Extended Hückel with self-consistence of the charge) in which parameters derived from X-ray data are used, we have modelized the thermal behaviour of the electric field gradient (EFG) tensor from 4 K to 300 K. The reduction in magnitude of electronic observables (e.g. spin orbit coupling constant and EFG magnitude) gave evidence for a dynamic Jahn-Teller effect. Spectra in a high magnetic field (6 teslas) confirmed the paramagnetic behaviour of the compounds. The sign of the EFG tensor, the magnetic hyperfine field tensor and its orientation with respect to the EFG tensor were determined.     

Synthesis,Spectral, Solvent Dependent Linear and Nonlinear Optical Characteristics of (E)-N-(3-(3-(4(dimethylamino)phenyl)acryloyl) phenyl)quinolone-2-carboxamide

This paper presents the synthesis of novel organic compound (E)-N-(3-(3-(4(dimethylamino)phenyl)acryloyl)phenyl)quinolone-2-carboxamide, also known as Quinolinecarboxamide Chalcone (QCC) using aldol condensation and carboxamide formation method. The organic sample QCC was examined by FT-IR, ¹H NMR, ¹³C NMR and mass spectroscopic techniques, respectively. Linear and third-order nonlinear optical (TNLO) properties of QCC dissolved in polar solvents such as DMSO, DMF and Ethanol have also been studied. The order of nonlinear refractive index and nonlinear absorption coefficient of QCC was measured to be 10^?11 m²/W and 10^?5 m/W. The nonlinear refractive index (n₂) of QCC was attributed to negative nonlinearity due to self-defocusing effect, and nonlinear absorption coefficient (β) indicates the behaviors of saturable absorption (SA) and reverse saturable absorption (RSA). The real and imaginary features of the TNLO susceptibility (χ⁽³⁾) of QCC in polar solvents were calculated to be the order of 10^─7 esu. The spectral characteristics of solvent on TNLO susceptibility of QCC were discussed. The results divulged that the synthesized organic compound is a novel nonlinear optical (NLO) material for applications in photonics and optoelectronics.

     

The high resolution rotational spectrum of 2-cyanoaziridine

The microwave spectrum of 2-cyanoaziridine has been measured and assigned. Only the spectrum of the cis isomer has been detected although extensive searches for transitions from the trans isomer have been made, suggesting that it is at least 11 kJ mol^?1 less stable. The following nuclear quadrupole coupling constants were obtained: χ_aa(1) = ?1.249(14), χ_bb(1) = 1.407(12), χ_aa(2) = ?3.547(6), χ_bb(2) = 1.865(8) MHz, the former pair probably referring to the amino nitrogen and the latter pair to the nitrile nitrogen. The rotational constants derived from the analysis are: A = 16877.718(32), B = 3528.931(4), C = 3373.065(4) MHz, D_N = 1.10(4) kHz.     

Two-dimensional spin freezing in Y1−z Ca z Ba2Cu3−x Fe x O7

Hyperfine electric and magnetic interactions in Y_1?z Ca _z Ba₂Cu_3?x Fe _x O_6+y compounds have been studied for different rates of Fe and Ca substitution (x=0.09 and 0.24;z=0.24;y=0?1) by⁵⁷Fe Mössbauer spectroscopy of powder samples obtained by different thermal treatments. Calculations of the Fe³⁺ EFG tensor have been performed for different coordination polyhedra in Cu1 and Cu2 sites. Variations of the direction, amplitude and of the sign of the principal component of the EFG are reported versus the iron displacement from the ideal Cu sites inside the pyramidal and tetrahedral coordination polyhedra. Calculated ΔE _Q and η values are compared with the experimental ones. For the Cu2 site, faithfully probed in both oxygen-depleted and oxygen-saturated samples by fairly large fraction of residing iron atoms, the mutual orientations of the axes of the principal EFG component and that of easiest magnetization are deduced from interrelations between quadrupole parameters for paramagnetic quadrupolar and magnetic Zeeman Mössbauer spectra. In the desoxygenated samples, the coexistence of a long range 2D antiferromagnetic order and of a spin-glass order has been evidenced. For the oxygen-saturated samples, the two-dimensional spin-glass order is observed belowT _f =10 K. The Mössbauer spectra under applied fields at 4.2 K show an easy polarization of the spins in the Cu2 sites.     

Temperature dependence of the electric field gradient in HfF4.HF.2H2O

The hyperfine quadrupole interaction in HfF₄.HF.2H₂O was studied using the time differential perturbed angular correlation (TDPAC) technique. The electric field gradient (EFG) and the corresponding asymmetry parameter were measured in the temperature range from 9 to 350 K. The EFG is characterized by a rather strong increase with temperature, whereas the asymmetry parameter reaches its maximum value (η≈1) at aboutT=160 K. At 420 K, the complex is dehydrated and looses HF: The quadrupole parameters determined from subsequent TDPAC measurements are charateristic for HfF₄.     

A CEMS study of ac-axis oriented thin film of YBa2(Cu0.97 57Fe0.03)3O7

⁵⁷Fe Mössbauer spectra of a fullyc-axis oriented epitaxial thin film of YBa₂(Cu_0.97 ⁵⁷Fe_0.03)₃O₇, recorded by CEMS, are reported. Spectra taken at different angles between the normal of the film (i.e. thec-axis) and the gamma ray direction show that for two of the three observed quadrupole doublets the main component of the EFG lies in thea?b-plane, for the third doublet it is parallel to thec-axis. The EFG of all three doublets has approximately axial symmetry.     

Beam maser measurement of deuterium quadrupole coupling in CD2F2

Hyperfine structure on the 2₂₀ → 3₁₃ rotational transition of CD₂F₂ was measured using a molecular beam maser spectrometer with 6 kHz linewidth (f.w.h.m.). The measured deuterium quadrupole coupling strength along the CD bond direction is eq_zzQ = 186 ± 10 kHz. The best fit asymmetry parameter is η = ?0.15 ± 0.05. Spin-rotation interaction strengths obtained from the spectrum are related to similar terms for CH₂F₂. The center frequency for the observed transition is 22 727 863 ± 2 kHz.     

Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds

Two hexanuclear niobium halide cluster compounds with a [Nb₆X₁₂]²⁺ (X=Cl, Br) diamagnetic cluster core, have been studied by a combination of experimental solid-state NMR/NQR techniques and PAW/GIPAW calculations. For niobium sites the NMR parameters were determined by using variable B_o field static broadband NMR measurements and additional NQR measurements. It was found that they possess large positive chemical shifts, contrary to majority of niobium compounds studied so far by solid-state NMR, but in accordance with chemical shifts of ⁹⁵Mo nuclei in structurally related compounds containing [Mo₆Br₈]⁴⁺ cluster cores. Experimentally determined δ_iso(⁹³Nb) values are in the range from 2400 to 3000 ppm. A detailed analysis of geometrical relations between computed electric field gradient (EFG) and chemical shift (CS) tensors with respect to structural features of cluster units was carried out. These tensors on niobium sites are almost axially symmetric with parallel orientation of the largest EFG and the smallest CS principal axes (V_zz and δ₃₃) coinciding with the molecular four-fold axis of the [Nb₆X₁₂]²⁺ unit. Bridging halogen sites are characterized by large asymmetry of EFG and CS tensors, the largest EFG principal axis (V_zz) is perpendicular to the X-Nb bonds, while intermediate EFG principal axis (V_yy) and the largest CS principal axis (δ₁₁) are oriented in the radial direction with respect to the center of the cluster unit. For more symmetrical bromide compound the PAW predictions for EFG parameters are in better correspondence with the NMR/NQR measurements than in the less symmetrical chlorine compound. Theoretically predicted NMR parameters of bridging halogen sites were checked by ^79/81Br NQR and ³⁵Cl solid-state NMR measurements.     

<Superscript>2</Superscript>H and <Superscript>13</Superscript>C NMR investigation of deuterofullerites C<Subscript>60</Subscript>D<Subscript>x</Subscript>

Deuterofullerites C₆₀D_x have been studied by ²H and ¹³C NMR. These fullerites have two types of carbon–deuterium bonds: C–D terminal bonds, characterized by the quadrupole coupling constant (QCC) of 171 kHz, and –C ··· D ··· C– bridging bonds with a QCC of 56 kHz. The latter is responsible for the rigid lattice found in these fullerites, which is untypical of fullerenes. PACS 81.05.Tp; 82.56.Fk; 61.48.+c; 61.18.Fs; 61.10.Nz     

Nuclear resonance measurements of CePd2Ga3

CePd₂Ga₃, a Kondo lattice exhibiting ferromagnetic order below T _C = 6.3 K, has been studied using Ga NMR technique. Measurements of the magnetic susceptibility on an oriented sample proved the strong anisotropy of this quantity, whose major component is in the basal plane. From the analysis of NMR spectra of differently oriented samples, the quadrupole parameters and the temperature-dependent anisotropic Knight-shift have been determined. While the anisotropy of the susceptibility can sufficiently account for the axial anisotropy of the ⁷¹Ga Knight shift, the in-plane anisotropy of the shift points towards dipolar effects enhanced by hybridization of the Ce-4f and Ga-s electrons.