Structure of B2O3 Glass at High Pressure: A 11B Solid-State NMR Study

We report spectroscopic evidence for the pressure-induced structural changes in B2O3 glass quenched from melts at pressures up to 6 GPa using solid-state NMR. While all borons are tri-coordinated at 1 atm, the fraction of tetra-coordinated boron increases with pressure, being about 5% and 27% in the B2O3 glass quenched from melts at 2 and 6 GPa, respectively. The fraction of boroxol ring species increases with pressure up to 2 GPa and apparently decreases with further compression up to 6 GPa. Two densification mechanisms are proposed to explain the variation of boron species with pressure.     

对含Y_2O_3和Gd_2O_3的La_2O_3-B_2O_3-BaO玻璃化学稳定性研究

本文研究了含Ｙ２Ｏ３和Ｇｄ２Ｏ３的Ｌａ２Ｏ３－Ｂ２Ｏ３－ＢａＯ玻璃的耐水性和耐酸性。结果表明，比硅酸盐玻璃化学稳定性差的Ｌａ２Ｏ３－Ｂ２Ｏ３－ＢａＯ玻璃，可以适量的用Ｙ２Ｏ３和Ｇｄ２Ｏ３取代Ｌａ２Ｏ３，可得以改善     

Quadrupole interactions at europium sites in Eu3V2O7 and Eu2VO4

The electric-quadrupole interactions at the Eu sites in Eu₃V₂O₇ and Eu₂VO₄ oxides have been studied at room temperature with¹⁵¹Eu Mössbauer spectroscopy. Both divalent and trivalent Eu ions were found in the oxides. The fraction of Eu²⁺ is 17.1(8)% in Eu₃V₂O₇ and 39.0(1.6) % in Eu₂VO₄. The values of the quadrupole coupling constant, eV_zzQ_g, obtained from the fits using a full Hamiltonian method are ?6.594(50) and ?8.043(65) mm/s for Eu³⁺, and ?13.168(402) and ?18.032(134) mm/s for Eu²⁺, respectively in Eu₃V₂O₇ and Eu₂VO₄. The magnitude of eV_zzQ_g in Eu₂VO₄ is the largest ever reported for Eu²⁺ in any Eu oxide system.     

Site discrimination in the crystalline borophosphate Na5B2P3O13 using advanced solid-state NMR techniques

A comprehensive solid-state NMR investigation on crystalline Na(5)B(2)P(3)O(13) is presented. Triple-quantum magic angle spinning (TQMAS) and rotational echo double resonance (REDOR) studies are used for accurate determinations of the (11)B, (23)Na and (31)P interaction parameters. Based on these results and complementary quantum mechanical calculations, plausible site assignments can be derived. Generally, the results show that detailed, quantitative information about structures in borophosphate compounds can be obtained by investigating both the local site environments characterized by chemical shift and quadrupolar interaction parameters and the correlated dipolar interactions to atoms in the second coordination sphere.     

Quadrupole interactions and relaxation effects in Dy2Ti2O7

Studies of quadrupole interactions and relaxation phenomena in Dy₂Ti₂O₇ at various temperatures up to 750 K have been performed using the Mössbauer effect of the 25.6 keV transition in ¹⁶¹Dy. The source used was ¹⁶¹Tb in ¹⁶⁰Gd₂Ti₂O₇ at 150 K, which emits a very narrow 25.6 keV γ line. Quadrupole interaction parameters and relaxation times, as function of temperature, were deduced from the measurements.     

Influence of the PLD parameters on the crystalline phases and fluorescence of Eu:Y2O3 planar waveguides

Eu³⁺-doped yttrium oxide (Eu:Y₂O₃) films were grown on fused-silica substrates by laser ablation. Depending on oxygen pressure, substrate temperature and laser energy density, the crystalline structure of the films, determined by X-ray diffraction and Raman spectroscopy, changes from monoclinic to cubic. The crystalline structure of the films is confirmed by Eu³⁺ fluorescence spectra and refractive indices, measured by m-line spectroscopy. The cubic crystalline films show low-loss waveguiding properties. PACS 81.15.Fg; 78.55.Hx; 78.20.Ci     

B3LYP Calculation of Deuterium Quadrupole Coupling Constants in Molecules

The B3LYP/6-31G(df,3p) model for the calculation of deuterium nuclear quadrupole coupling constants (nqcc's) is shown to yield results as accurate as calculations previously performed at the MP4 level of theory. For 25 molecules, ranging from HD and DF to pyridine and fluorobenzene, the rms difference between the B3LYP nqcc's and the experimental nqcc's is 3.2 kHz (2.7%). For benzene, our calculations suggest that the experimental χ_bband χ_ccof S. Jans-Bürli, M. Oldani, and A. Bauder, 1989.Mol. Phys.,68, 1111–1123) have been incorrectly assigned with respect to inertia axes and should be reversed. For borane carbonyl and nitric acid, it is shown that nqcc calculations using hydrogen bond lengths given by MP2/6-311 + G(d,p) optimizations in combination with the heavy atom experimental structures significantly improve agreement with the experimental nqcc's.     

Nd3+掺杂B2O3-Nb2O5-BaO-La2O3玻璃光谱性质的研究

 用高温熔融法制备了Nd³⁺(物质的量分数2％）掺杂40B₂O₃-(15-χ)Nb₂O₅-45BaO-χLa₂O₃玻璃，测量了样品的吸收光谱、发射光谱和差热分析（DTA）曲线。根据Nd3+光学跃起矩阵的特点，应用Judd-Ofelt理论，从吸收光谱获得了Nd³⁺光学跃起的强度参数。并计算了Nd³⁺离子的自发辐射跃迁几率、总自发辐射几率、荧光分支比、辐射能级寿命和受激发射截面。结果表明：该体系玻璃中，随着Nb₂O₅ 含量的增加和La₂O₃₂增大，说明材料的对称性降低；而Ω₆减小，说明Nd-O键的共价性和键强增强；受激发射截面减小。DTA实验表明，随着Nb₂O₅含量的增加，材料的热稳定性提高。     

Optical Properties of Yb3+ Doped Bi2O3-3B2O3 Glass

The transmission and fluorescence spectra of Yb3+ doped Bi2O3-3B2O3 glass were measured. The emission cross section have been evaluated using the measured absorption apectra and principle of reciprocity. The measured long lifetime τm(1.0 ms) and large emission cross section σem(1.423 pm2) indicate that Yb3+ doped Bi2O3-3B2O3 glass is a promisiong laser material.     

An anomalous enhancement in the electrical conductivity of Li2O : B2O3 : Al2O3 glasses

The study of electrical conductivity of 27.5 Li₂O : (72.5 − x) B₂O₃ : x Al₂O₃ glass samples has been carried out. It has been observed that the conductivity exhibits Arrhenius behavior for all samples up to glass transition temperature T_g. Beyond T_g, an anomalous enhancement followed by decrease in conductivity has been observed. The results have been explained by dividing the temperature range into two regions. In region-I, it has been observed that the conductivity variation exhibits a maximum at 2.5 mol% Al₂O₃, which has been explained on the basis of Mixed Glass Former Effect (MGFE). An anomalous enhancement in the conductivity observed in region-II has been attributed to the nucleation in the glass. The subsequent decrease in the conductivity has been attributed to the crystallization of the glass samples.     

Magnetic properties of xCoO.(1-x)[2B2O3.K2O] glasses

The results of magnetic investigations onxCoO.(1-x)[2B₂O₃.K₂O] glasses are reported. The magnetic properties of these glasses are dependent on the CoO content. For glasses withx > > 10 mol% CoO, the Co²⁺ ions are coupled antiferromagnetically.     

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic evidence of polymorphism in vitreous B2O3

Brillouin and Raman spectroscopy were performed on B2O3 glass compressed to 57 GPa at 273 K. Upon compression the sound velocities increase smoothly and the boroxol ring Raman mode vanishes by 11 GPa. Upon decompression the sound velocities follow a different path and at 3 GPa a discontinuity of 3 km/s in V(p) and 2 km/s in V(s) returns the velocities to the values seen on compression. After the transition, the boroxol ring Raman mode reappears. A second pressure cycle produces the same behavior, suggesting the 3 GPa transition occurs between vitreous polymorphs with different boron coordination.     

Spin valve effect and magnetoresistivity in single crystalline Ca3Ru2O7

The laminar perovskite Ca3Ru2O7 naturally forms ferromagnetic double layers of alternating moment directions, as in the spin-valve superlattices. The mechanism of the huge magnetoresistive effect in the material has been controversial due to a lack of clear understanding of various magnetic phases and phase transitions. In this neutron diffraction study in a magnetic field, we identify four different magnetic phases in Ca3Ru2O7 and determine all first-order and second-order phase transitions between them. The spin-valve mechanism then readily explains the dominant magnetoresistive effect in Ca3Ru2O7.