Second-order optical non-linearity initiated in Li2O–Nb2O5–SiO2 and Li2O–ZnO–Nb2O5–SiO2 glasses by formation of polar and centrosymmetric nanostructures

Amorphous nanoheterogeneities of the size less than 100 Å have been formed in glasses of the Li₂O–Nb₂O₅–SiO₂ (LNS) and Li₂O–ZnO–Nb₂O₅–SiO₂ (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher T_g lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO₃ and non-polar LiZnNbO₄ in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO₃) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO₄) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO₃ crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Role of Te valence on phases crystallized in K2O–Nb2O5–TeO2 glasses

Differences in crystalline phases between glass-ceramics and sintered ceramics in the K₂O–Nb₂O₅–TeO₂ system have been examined, particularly to obtain information on the role of Te valence on crystallization behaviors of TeO₂-based glasses. In glasses or glass-ceramics, the valence of Te⁴⁺ is retained even during heat-treatment up to around 600°C, leading to the formation of crystalline phases containing Te⁴⁺, e.g., the face-centered cubic crystalline phase. In a powder sintering method, Te⁴⁺ is easily oxidized to Te⁶⁺ during sintering at around 600°C in air and compounds such as KNbTeO₆ in which Te⁶⁺ is present are formed.     

Influence of thermal and thermoelectric treatments on structure and electric properties of B2O3–Li2O–Nb2O5 glasses

A transparent glass with the composition 60B₂O₃–30Li₂O–10Nb₂O₅ (mol%) was prepared by the melt quenching technique. The glass was heat-treated with and without the application of an external electric field. The as-prepared sample was heat-treated (HT) at 450, 500 and 550 °C and thermoelectric treated (TET) at 500 °C. The following electric fields were used: 50 kV/m and 100 kV/m. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, dc and ac conductivity, as a function of temperature, were used to investigate the glass and glass-ceramics properties. LiNbO₃ crystals were detected, by XRD, in the 500 °C HT, 550 °C HT and 500 °C TET samples. The presence of an external electric field, during the heat-treatment process, improves the formation of LiNbO₃ nanocrystals at lower temperatures. However, in the 550 °C HT and in the TET samples, Li₂B₄O₇ was also detected. The value of the σ_dc decreases with the rise of the applied field, during the heat-treatment. This behavior can indicate an increase in the fraction of the LiNbO₃ crystallites present in these glass samples. The dc and ac conduction processes show dependence on the number of the ions inserted in the glass as network modifiers.The Raman analysis suggests that the niobium ions are, probably, inserted in the glass matrix as network formers.These results reflect the decisive effect of temperature and electric field applied during the thermoelectric treatment in the structure and electric properties of glass-ceramics.     

Characteristics and biocompatibility of Na2O–K2O–CaO–MgO–SrO–B2O3–P2O5 borophosphate glass fibers

A novel Na₂O–K₂O–CaO–MgO–SrO–B₂O₃–P₂O₅ borophosphate glass fiber is prepared. The thermal properties including differential thermal analysis (DTA) and viscosity measurement of the glass were presented. The tensile strength of the glass fiber is measured. The reaction of the glass fibers in the SBF solution is characterized by XRD, FTIR and SEM. XRD and FTIR indicate that the carbonate hydroxyapatite has formed rapidly on the glass. Cell attachment, spreading and proliferation on the glass are determined by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay method using Human osteosarcoma MG-63 cells. The bioactivity and biocompatibility of the glass fiber make it a good potential prospect in the field of tissue engineering.     

Studies of ternary Li2SO4–Li2O–P2O5 glasses

Glasses in a wide range of compositions in the ternary system xLi₂SO₄–yLi₂O–zP₂O₅ where x ranges from 0 to 30 mol%, y ranges from 35 to 55 mol% and z ranges from 25 to 50 mol% have been prepared and their properties measured using infra-red, Raman, and ³¹P magic angle spinning nuclear magnetic resonance spectroscopic techniques. We conclude that a random close packing of phosphate and sulphate ions which also leads to formation of connected voids in the structure is consistent with our data. There is also evidence for formation of condensed sulphate–phosphate species in the liquid which may be retained in the glass structure.     

Raman and NMR study of bioactive Na2O–MgO–CaO–P2O5–SiO2 glasses

The results of a structural study combining NMR and Raman spectroscopy of several melt-derived glasses in the system Na₂O–MgO–CaO–P₂O₅–SiO₂ are presented. The Raman spectra show clear changes in the Si–O–Si vibrational modes (related to the bridging oxygen atoms, BO) and also verify the presence of non-bridging oxygen atoms (NBO), also named terminal oxygens. The intensity of the Si–O–NBO stretching mode depends on the cation concentration. It can be concluded from the NMR studies that the MgO-containing samples have orthophosphate units charge-compensated by Ca²⁺ and Mg²⁺. The silicate matrix also contains both types of two-valent cations and consists of Q² and Q¹ units. Similarly, the Na₂O-containing samples contain isolated orthophosphate units in a silicate matrix (Q² and Q³ units), both charge-compensated by mixed cations Ca²⁺ and Na⁺. These experimental data were compared with theoretical parameters given by the Stevels model, which is a suitable tool for understanding bioactive behavior of these glasses. Furthermore, results of the in vitro tests carried out in simulated body fluids are presented and compared with both Raman and NMR structural data.     

Structure of V2O5–P2O5 glasses by X-ray and neutron diffraction

The atomic structures of two V₂O₅–P₂O₅ glasses and vitreous (v-) V₂O₅ were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VO_n units that constitute the structures of the glasses. VO₅ square pyramids with elongated bonds of ~ 0.190 nm to the pyramidal base are found for the 50V₂O₅–50P₂O₅ glass. These weaker V–O bonds are balanced in V–O–P bridges by overbonded P–O bonds. The V^(IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V₂O₅–27P₂O₅ and 50V₂O₅–50P₂O₅ glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO)₂P₂O₇. The short-range structure of v-V₂O₅ and the 73V₂O₅-27P₂O₅ glass is formed of mixtures of VO₅ and VO₄ pyramids. A significant amount of V···O distances > 0.22 nm found for all glasses belong either to linkages V=O···V or to three-coordinated O sites.     

IR and ESR investigations on V2O5–P2O5–BaO glass system with opto-electronic potential

The changes observed in the IR and ESR spectra of the xV₂O₅(1 ? x)[0.8P₂O₅ ? 0.2BaO] glass system with 0 ≤ x ≤ 50 mol% show that vanadium oxide acts as a network modifier at low concentration (x ≤ 5 mol%) and as a network former for high content (x ≥ 10 mol%). Thus the IR bands belonging to the phosphate groups are strongly reduced except the specific bands of the short chain phosphate units due to the phosphate network depolymerization and the spectra are dominated by the vibrations characteristic for POP, POV and VOV linkages. At the same time the changes observed in the ESR spectra of these glasses are explained supposing the superposition of two signals, one with a well-resolved hyperfine structure typical for isolated V⁴⁺ ions and a broad line characteristic for clustered ions. The line width dependence versus V₂O₅ content shows that dipole–dipole interactions exist between vanadium ions until x = 5 mol% and the superexchange interactions prevail at high content (x > 10 mol%).     

Y2O3添加对Nb2O5低膨胀陶瓷结构与性能的影响

采用高温固相烧结法制备了Y2O3改性Nb2O5低膨胀陶瓷材料.研究了Y2O3添加量对Nb2O5陶瓷的物相组成、微观结构、气孔率、热膨胀性能、抗弯强度和抗热震性能等的影响.结果表明,经1390℃保温2h烧成,纯Nb2O5陶瓷样品存在开裂现象,表现出低的抗弯强度和差的抗热震性能.添加2～ 10;Y2O3后,样品主晶相为单斜相Nb2O5,还生成了YNbO4晶相.通过添加适量Y2O3改性,可抑制Nb2O5陶瓷烧成过程中的晶粒增长和避免开裂现象,形成致密的微观结构,样品的抗弯强度和抗热震性能显著提高.Nb2O5陶瓷的热膨胀系数随Y2O3添加量的增加而逐渐增大.Y2O3添加量为6;时,样品的热膨胀系数和抗弯强度分别为1.9×10-6/℃和103.4 MPa,表现出良好的抗热震性能.     

Effect of alumina on the structure and properties of Li2O–B2O3–P2O5 glasses

The structure of glasses within the system Li₂O–Al₂O₃–B₂O₃–P₂O₅ has been studied through ³¹P, ¹¹B and ²⁷Al Nuclear Magnetic Resonance, and the effect of Al₂O₃ substitution by B₂O₃ and P₂O₅ network formers on the structure and properties investigated for a constant Li₂O content. Multinuclear NMR results reveal that substitution of Al₂O₃ for B₂O₃ and P₂O₅ network formers in a glass with composition 50Li₂O·15B₂O₃·35P₂O₅ produces a change in boron environment from four-fold to three-fold coordination. Meanwhile aluminum can be present in four-, five- and six-fold coordinations a higher amount of Al(IV) groups is found for increasing alumina contents. The behavior of the glass transition temperature and electrical conductivity of the glasses has been interpreted as a function of the structural changes induced in the glass network when alumina is substituted for B₂O₃, P₂O₅ or both. Small additions of alumina produce a drastic increase in glass transition temperature, while it does not change for [Al₂O₃] greater than 3 mol.%. However, the electrical conductivity shows very different behavior depending on the type of substitution; it can remain constant when B₂O₃ content decreases or sharply decrease when P₂O₅ is substituted by Al₂O₃, which is attributed to a higher amount of BO₃ and phase separation.     

Composition analysis of glasses in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

Composition change during the melting process of some glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system melted at 450–470°C for 15 min was studied. Results show that there was a remarkable difference between the batch composition and the analyzed composition. Large amount of P, Br, Pb, and Cl were lost mainly in the form of PbBr₂, PbCl₂ and P₂O₅. The content of O is influenced by two factors. The incomplete decomposition of NH₄H₂PO₄ or the reaction between P₂O₅ and H₂O in the atmosphere increases the content of O, while the volatilization of P₂O₅ decreases the content of O.     

Thermal and electric transport properties of (60−x)V2O5–xAs2O3–20Fe2O3–10CaO–10Li2O unconventional glassy system

This paper presents the results of kinematical studies of glass transition and crystallization in the unconventional glassy system (60?x)V₂O₅–xAs₂O₃–20Fe₂O₃–10CaO–10Li₂O (x = 0, 10, 20, 30, 40 mol%) using differential scanning calorimetry (DSC). The glass transition temperatures (T_g), the onset crystallization temperatures (T_c), and the peak temperatures of crystallization (T_p) were found to be dependent on the compositions and the heating rates. From the dependence on heating rates of (T_g) and (T_p) the activation energy for glass transition (E_g) and the activation energy for crystallization (E_c) are calculated. The thermal stability of (60?x)V₂O₅–xAs₂O₃–20Fe₂O₃–10CaO–10Li₂O was evaluated in term of, criteria ΔT = T_c ? T_g. All the results confirm that the thermal stability increase with increasing As₂O₃ contents. From the electric–dielectric measurements it was found that, σ_dc, σ_ac(ω) and θ_D/2 decrease with increasing As₂O₃ contents. It is also observed that the dielectric constant (ε₁(ω)) and the loss factor (tan δ) decrease with increasing As₂O₃ contents in this glass system.     

Microstructural characteristics and crystallization of CaO–P2O5–Na2O–ZnO glass ceramics prepared by sol–gel method

Porous phosphate-based glass ceramics prepared by the sol–gel method were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential thermal analysis (DSC). The 48CaO–45P₂O₅–2ZnO–5Na₂O glassy system can remain fully amorphous up to 550 °C. After heat treated at 650 °C, the obtained porous bodies consisted of dense struts and macropores where β-Ca₂P₂O₇ and Na₂CaP₂O₇ phases crystallized from the glass matrix. When treated at 750 °C, Ca₄P₆O₁₉ and NaZn(PO₃)₃ precipitated homogeneously as new phases among the residual glass matrix. The material was assessed by soaking samples in phosphate-based buffer solution (PBS) solution to determine the solubility and observe apatite formation.     

Glass forming region and physical properties in the system P2O5-Na2O–Fe2O3

The glass forming region of the system P₂O₅–Na₂O–Fe₂O₃ was determined, using phosphate salts as precursor materials. The glasses were produced in non-wetting gold/platinum crucibles in order to avoid contamination. Glass formation was confirmed using XRD and the final composition determined using EDX. The glass forming region was found to be relatively short at 50% P₂O₅ content in comparison to both lower and higher P₂O₅ content. As expected, the inclusion of Fe₂O₃ had a significant effect on both glass transition temperature and density with a peak seen at around 30 mol% Fe₂O₃. This coincides with previously reported abrupt structural changes in the glass. The inclusion of Na₂O has little effect on the glass transition temperature but causes a small increase in density.     

熔盐法合成SrBi2Nb2O9粉体

以分析纯的Bi2O3,Nb2O5 和 SrCO3为原料,以KCl和NaCl为熔盐,采用熔盐法在800～1000 ℃合成了片状SrBi2Nb2O9粉体.研究了熔盐含量及合成温度对晶体定向生长和粉体形貌的影响.结果表明:与固相法相比,熔盐法是一种有效的晶粒定向生长的方法.制备的粉体呈明显的片状和高度的各向异性,且无团聚现象产生.沿(00l)面择优生长适合的熔盐含量为60;质量分数,随着熔盐含量的增加,晶粒尺寸逐渐增大.合成温度在900 ℃为最优,可获得较大尺寸和高度各向异性的SrBi2Nb2O9粉体.     

Temperature dependent blue second harmonic generation in Ba5Li2Ti2Nb8O30 microcrystals embedded in TeO2 glass–matrix

The as-quenched samples in the system (100 ? x) TeO₂-(x) Ba₅Li₂Ti₂Nb₈O₃₀ (2 ? x ? 8) were found to be embedded with 10–20 μm sized crystallites of the polar phase Ba₅Li₂Ti₂Nb₈O₃₀ (BLTN). Blue (400 nm) second harmonic generation (SHG) was observed in transmission mode when 800 nm laser light was allowed to pass through the individual crystallites. The blue SHG signal was temperature dependent and its intensity was maximum at ～175 °C which was tentatively attributed to the concomitant changes associated with the refractive indices of the BLTN crystallites. The SHG intensity attained a minimum value around the Curie temperature of BLTN crystals.     

Magnetite nanoparticles prepared by the crystallization of Na2O–Fe2O3–B2O3–SiO2 glasses

A glass with the composition of 35Na₂O–24Fe₂O₃–20B₂O₃–20SiO₂–1ZnO (mol%) was melted, quenched, using a twin roller technique, and subsequently heat treated in the range 485–750 °C for 1–2 h. This led to the crystallization of magnetite as the sole or the major crystalline phase.Heat treatment at lower temperatures resulted in the crystallization of magnetite crystals 7–20 nm in diameter, whereas heat treatment at higher temperatures produced higher quantities of magnetite and much larger crystals. The room temperature magnetization and coercive force values were in the range of 6–57 emu g^? 1 and 0–120 Oe, respectively for the heat treated glasses.     

The effect of ionic and metallic silver on the crystalline phases developed in CaO–Al2O3–TiO2–P2O5 glasses

Development of crystallization in the CaO–Al₂O₃–TiO₂–P₂O₅ system glasses was investigated in the presence of ionic and metallic silver. Differential thermal analysis, X-ray diffractometry, ultra violet–visible spectrophotometry, atomic force microscopy and scanning electron microscopy were used to evaluate the resulted glasses and glass-ceramics. It was found that silver ions facilitated crystallization by decreasing the viscosity of the glasses. However, metallic silver, which was formed through heat treatment in hydrogen atmosphere, improved heterogeneous crystallization of the reduced glasses in the subsequent heat treatment. The preformed metallic silver led to effective crystallization of calcium titanium phosphate (CaTi₄(PO₄)₆), calcium metaphosphate (Ca(PO₃)₂) and calcium pyrophosphate (Ca₂P₂O₇) phases at significantly decreased temperatures. The two latter phases were partially dissolved out by leaching in acidic solution and left out a porous structure of calcium titanium phosphate glass-ceramic.     

Nb2O5掺杂对Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3陶瓷组织与性能的影响

采用固相烧结法制备Nb2O5掺杂的Pb(Mg1/3Nb2/3) O3-PbZrO3-PbTiO3+ 0.5mol; ZnO(PMN-PZT)压电陶瓷,研究了不同Nb2O5掺杂量对材料结构及压电介电性能的影响.实验结果表明,随着Nb2O5掺杂量的增加(0～1 mol;),PMN-PZT陶瓷的晶界强度提高,断裂模式由沿晶断裂逐渐转变为穿晶断裂,而且陶瓷的压电介电性能升高.当Nb2O5掺杂量为1mol;时,1250℃烧结的陶瓷样品性能参数为:d33=430 pC/N,Qm=60,kp=0.52,kt=0.38,εr=3620,tanδ=0.017.