Glass formation and optical properties of glasses in the systems (R2O or R''O)-Ta2O5---Ga2O3

Gallate glasses containing no conventional glass formers were obtained in the systems (Na₂O, K₂O or Cs₂O)-Ta₂O₅---Ga₂O₃ and (Sr or BaO)-Ta₂O₅---Ga₂O₃ by an ordinary crucible-melting technique. The glasses showed high optical transmission in the infrared as well as in the visible region. Infrared spectroscopic analysis suggested that the Ga³⁺ ions are tetrahedrally coordinated in the glasses. The glass-forming tendency of the melt and the infrared transmission of the glasses are discussed in terms of the glass structure.     

The effect of MgO on the thermodynamics of the Fe/Fe-redox equilibrium and the incorporation of iron in soda-magnesia-aluminosilicate melts

Melts with the basic compositions 10Na₂O · 10MgO · xAl₂O₃ · (80−x)SiO₂ (x=0, 5, 10, 15 and 20), 10Na₂O · xMgO · 10Al₂O₃ · (80−x)SiO₂ (x=5, 10, 15 and 20) and xNa₂O · 10MgO · 10Al₂O₃ · (80−x)SiO₂ (x=5, 10 and 15) all doped with 0.25 mol% Fe₂O₃ were studied using square-wave voltammetry. The temperatures applied were in the range of 1000–1600 °C. The square-wave voltammograms recorded show peaks caused by the reduction of Fe³⁺ to Fe²⁺. The attributed peak potentials measured decreased linearly with decreasing temperatures. Increasing the MgO-concentration led to more negative peak potentials. Introducing alumina in the melt first resulted in less negative peak potentials. If the molar Al₂O₃-concentration is equal to that of Na₂O (=10 mol%) the peak potentials are least negative. Further increase of the Al₂O₃-concentration led to more negative peak potentials. The variation of the Na₂O-concentration led to a maximum in the peak potentials at an Na₂O-concentration of 10 mol%. An empirical formula which allows the calculation of standard potentials from the chemical composition is proposed. Furthermore, a structural explanation for the effect of the chemical composition is given. Especially, the incorporation of Al₂O₃ as AlO₄⁻-tetrahedra at [Al₂O₃] < [Na₂O] and as network modifier at larger concentrations was structurally explained by the similarities of Fe²⁺ and Mg²⁺, with respect to cation radii and metal–oxygen bond lengths.     

Precipitation of In2O3 nano-crystallites from glasses in the system Na2O/B2O3/Al2O3/In2O3

Glasses in the system Na₂O/B₂O₃/Al₂O₃/In₂O₃ were melted and subsequently tempered in the range from 500 to 700 °C. Depending on the chemical composition, various crystalline phases were observed. From samples without Al₂O₃, In₂O₃ could not be crystallized from homogeneous glasses, because either spontaneous In₂O₃ crystallization occurred during cooling, or other phases such as NaInO₂ were formed during tempering. The addition of alumina, however, controlled the crystallization of In₂O₃. Depending on the crystallization temperature applied, the crystallite sizes were in the range from 13 to 53 nm. The glass matrix can be dissolved by soaking the powdered glass in water. This procedure can be used to prepare nano-crystalline In₂O₃-powders.     

Effect of CaO on the surface morphology and strength of water soaked Na2O–B2O3–Al2O3–SiO2 vitrified bond

The surface morphology of Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂ vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C.     

Determination of Na2O activities in silicate melts by EMF measurements

An EMF cell using a Na-β″-alumina electrolyte has been designed for the quantification of the thermodynamic activity of Na₂O (aNa₂O) in a series of sodium-bearing silicate liquids at high temperature. Initial experiments have been performed using Na₂O–0.663WO₃ and Na₂O–0.555MoO₃ as reference liquids. Values of aNa₂O derived for Na₂O–2SiO₂ binary melt are found to be in excellent agreement with data from the literature, confirming the validity of the method. To extend use of this experimental set-up to higher temperature, the aNa₂O of industrial C-glass has been calibrated as a reference liquid at temperatures up to 1263 °C. The influence of additions of CaO, Al₂O₃ and B₂O₃ on the Na₂O activity of binary sodium-silicates has been quantified. For each glass composition, measured values of aNa₂O are a function of temperature, log(aNa₂O) varying as a function of inverse absolute temperature. Activation energies derived from these data are all generally similar with the exception of industrial E-glass, which is rich in Al and poor in Na. At constant temperature, additions of network forming Al₂O₃ and B₂O₃ to a Na₂O–SiO₂ binary melt yield a decrease of the activity of Na₂O, while addition of network modifying CaO results in an increase in (aNa₂O). These changes are qualitatively consistent with predictions based upon expected modifications of melt structure. However, measured values of log(aNa₂O) do not correlate perfectly with theoretical models of glass basicity, suggesting that either sodium activity is decoupled from melt basicity, or that current models are insufficient to calculate that parameter, in particular for the case of liquids poor in Na and rich in Al.     

Study of PbO films on sodium borate glasses part II: Formation of interdiffusion layers at the glass surface

By selecting carefully controlled conditions for the thermal treatment of sodium borate glasses coated with PbO films, it is possible to prevent Pb²⁺ ions from penetrating deeply into the glass. For low alkali glasses, an interdiffusion layer can be formed, which sub-surface cation profiling (by ion beam induced radiation) shows is a solid solution of Na₂O and B₂O₃ in PbO which acts as solvent. Experiments with 18.0 mol-% Na₂O glass show that it is possible to transform such an interdiffusion layer into a second type in which Na₂O and B₂O₃ together act as solvent and the concentration of PbO solute varies through the layer. For both types of layer the Na₂O : B₂O₃ ratio is different from that of the glass substrate, and for the production of the second type of layer it is shown that an important factor connected with penetration of PbO into the glass surface is a “sweating” process in which thermal treatment of the glass, even in the absence of PbO, results in migration of Na⁺ ions so that the glass surface has a Na₂O content higher than that of the bulk glass. Changes in the UV spectra of the Pb²⁺ ion are correlated with the formation of the interdiffusion layers, and results show that types of layer have optical basicities significantly greater than that of the glass substrate, through either the high PbO or high Na₂O content.     

Nuclear magnetic resonance studies of alkaline earth phosphosilicate and aluminoborosilicate glasses

The ¹¹B, ²⁷Al, ²⁹Si and ³¹P magic angle spinning (MAS) NMR spectra of MO–P₂O₅, MO–SiO₂–P₂O₅ and MO(M^′₂O)–SiO₂–Al₂O₃–B₂O₃ (M=Mg, Ca, Sr and Ba, M^′=Na) glasses were examined. In binary MO–P₂O₅ (M=Ca and Mg) glasses, the distributions of the phosphate sites, P(Q_n), can be expressed by a theoretical prediction that P₂O₅ reacts quantitatively with MO. In the ternary 0.30MO–0.05SiO₂–0.65P₂O₅ glasses, the 6-coordinated silicon sites were detected, whose population increases in the order of MgOxCaO–0.05SiO₂–(0.95−x)P₂O₅ glasses, its population increases with an increase in f (=([P₂O₅]−[MO]−[B₂O₃]−[Na₂O])/[SiO₂]) and has maximum at f=9. The signal due to the 5-coordinated silicon atoms is also observed when x is smaller than 0.45. When three network-forming oxides such as SiO₂, Al₂O₃ and B₂O₃ coexist, Al₂O₃ reacts preferably with MO. The populations of 4-coordinated boron atoms, N₄, are expressed well with r/(1−r), where r=([Na₂O]−[Al₂O₃])/([Na₂O]−[Al₂O₃]+[B₂O₃]). The correlation of the Raman signal at 1210 and 1350 cm⁻¹ with the NMR signal of Si(Q₆) at −215 ppm is also seen.     

Properties and structure of RO---Na2O---Al2O3---P2O5 (R = Mg, Ca, Sr, Ba) glasses

The properties and structure of (45 - x)RO · xNa₂O · 2.5Al₂O₃ · 52.5P₂O₅ (R = Mg, Ca, Sr, Ba, 0 x 31 mol%) glasses were investigated. The variation in the molar volumes of glasses in the MgO series is closely related to the formation of the end groups in the glasses with the substitution of Na⁺ ions for Mg²⁺ ions, resulting in a variation of the density and refractive index of the glasses. The properties of glasses containing CaO in terms of Na₂O substitution depend mainly on the low field strength of Na⁺ ions substituting for CaO even though the end groups occurring in the glasses increased. The variation in properties of the glasses containing SrO and BaO, some of which were substituted by Na₂O, could be explained by differences in masses, field strength and polarizability between the Na⁺ ions and the alkaline-earth ions due to a small variation in the structure of the glasses despite Na₂O substitution.     

Preparation and physical properties of amorphous V2O5 containing TiO2, Na2O or Li2O

V₂O₅ gels containing up to 18 mol% of TiO₂ were obtained through the simultaneous hydrolysis of alkoxides in ethanol solution. V₂O₅ gels containing Na₂O or Li₂O were obtained through the ion exchange method. The crystallization temperature, T_cr, of the gels increased and the H₂O content of the gels decreased by the addition of TiO₂ or Na₂O. These additives seem to stabilize the amorphous state of the gels. On the other hand, T_cr and the H₂O-content slightly varied with the addition of Li₂O. No ionic polarization was observed in coating films of the gels dried at temperatures below T_cr. The dc conductivity of the films was anisotropic, and increased with the addition of Li₂O or Na₂O. However, it decreased with increasing TiO₂ content. The fiber-like structure of gels was observed by TEM. The gels obtained from alkoxides were thin and short in comparison with the gels obtained through the ion exchange method.     

On the mechanism of electrical relaxation in Na-conductive phosphate glasses

The crossover from a frequency independent to a frequency dependent ac response has been studied in glasses with the composition 37.2Na₂O-12.8CaO₅ · 50P₂O₅ and 30Na₂O-5CaO-7.5Al₂O₃-57.5P₂O₅ (mol%) containing 5 × 10⁻³ ≤ mol% Ag₂O ≤ 5 × 10⁻¹. Recently, we have established that in these glasses the diffusion coefficient of guest silver ions varies in space. In this case, as a first approximation, the diffusion coefficient may be considered as a constant within regions whose size is no less than 10 nm across. We assume that the diffusion of sodium ions can be given by the D(r) coefficient with the same spatial dispersion as that of silver ions. It is demonstrated that the frequency dependence of ac response is in fair agreement with the assumption.     

Hydrolytic resistance of Na2O---B2O3---SiO2 gels prepared by sol-gel process

Alkoxide derived gels were prepared in the system Na₂O---B₂O₃---SiO₂. The gel compositions were situated in the liquid-liquid immiscibility area of the phase equilibrium diagram.

Hydrolytic resistance tests were performed on the gels heat-treated at temperatures ranging between 120 to 850 °C. The Na₂O, B₂O₃ and SiO₂ extracted from the attack gels were analyzed. The experimental results indicate that the amount of B₂O₃ has a significant influence on the chemical durability of the heat-treated gels. At temperatures of 850 °C the greater the B₂O₃ mol% the greater are the amounts of Na₂O and B₂O₃ extracted. Different behaviour was observed for gels heat-treated at 600 °C where the amounts of B₂O₃ and Na₂O extracted slightly increases as the B₂O₃ mol% increases. Small amounts of extracted SiO₂ were always observed.

These results are complemented with other measurements so that an explanation of the controlling mechanism is given.     

氧分压调控氧化铜薄膜生长及其表面功函数研究

本文采用反应磁控溅射法制备p型二元铜氧化物半导体薄膜,通过氧气流量调节实现Cu₂O、CuO和Cu₄O₃薄膜的可控生长。所制备薄膜的形貌与结构分别利用扫描电子显微镜、X射线衍射仪以及拉曼光谱进行表征。经紫外可见分光光度计测量可知,Cu₂O、CuO和Cu₄O₃薄膜的带隙分别为2.89 eV、1.55 eV和2.74 eV。为进一步研究Cu₂O、CuO和Cu₄O₃薄膜的表面物理性质,基于Kelvin探针力显微镜(KPFM)技术直接测量了薄膜样品与探针尖端间的接触电位差(V_CPD),结果表明Cu₂O、CuO和Cu₄O₃薄膜的表面功函数都随着温度的升高而呈现逐渐减小的趋势。     

铝源种类对熔盐法制备超细ZnAl2O4粉体的影响

本文以Al(OH)₃、煅烧Al₂O₃和纳米Al₂O₃为铝源,在KCl和LiCl的混合熔盐介质中,800~1 200 ℃温度范围内保温3 h合成超细ZnAl₂O₄粉体。采用XRD、SEM、激光粒度仪和比表面分析仪等重点分析了铝源种类对ZnAl₂O₄粉体合成温度、产物物相组成以及显微形貌的影响。在此基础上探讨了反应温度、熔盐与原料的质量比(W_s/W_r)对粉体合成的影响。结果表明:铝源种类显著影响ZnAl₂O₄的开始形成温度和粉体性能,相比于煅烧Al₂O₃,以Al(OH)₃和纳米Al₂O₃为铝源生成ZnAl₂O₄的速率较快,在900 ℃时即可合成出单相ZnAl₂O₄。以煅烧Al₂O₃粉为铝源,当W_s/W_r为3∶1时,在1 000 ℃合成ZnAl₂O₄粉体的分散性最佳,而温度过高易造成粉体团聚长大。适当的W_s/W_r有利于ZnAl₂O₄的生成,当W_s/W_r为4∶1时合成的ZnAl₂O₄粒径最小。ZnAl₂O₄粉体均在一定程度保持着初始铝源的尺寸和形貌,表明熔盐法合成ZnAl₂O₄的机理主要遵循着“模板合成机理”。     

TOPCon太阳电池发射极Al2O3/SiNx与SiO2/Al2O3/SiNx叠层膜钝化性能的比较

本文对TOPCon电池发射结的叠层钝化膜进行了研究,对比了3种不同叠层钝化膜(SiO₂/SiN_x、Al₂O₃(1.5 nm)/SiN_x、SiO₂/Al₂O₃(1.5 nm)/SiN_x)的钝化性能。结果表明:Al₂O₃(1.5 nm)/SiN_x的钝化性能优于SiO₂/SiN_x,SiO₂/Al₂O₃(1.5 nm)/SiN_x的钝化水平最佳,隐开路电压均值可达到705 mV。基于Al₂O₃/SiN_x叠层膜研究了Al₂O₃厚度(1.5 nm、3 nm和5 nm)对钝化性能和电池转换效率的影响。当Al₂O₃厚度由1.5 nm增加到3 nm时,钝化性能得到明显提升,隐开路电压均值提高了20 mV,达到707 mV,对应电池的光电转换效率升高了0.23个百分点,与SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜电池的转换效率持平。然而,当Al₂O₃厚度继续增加至5 nm时,隐开路电压均值保持不变。因此可以使用Al₂O₃(3 nm)/SiN_x叠层膜代替SiO₂/Al₂O₃(1.5 nm)/SiN_x叠层膜,不仅简化了电池的工艺步骤,而且降低了生产成本。     

雾化辅助化学气相沉积法氧化镓薄膜生长研究

采用自主设计搭建的雾化辅助化学气相沉积系统设备,开展了Ga₂O₃薄膜制备及其特性研究工作。通过X射线衍射研究了沉积温度、系统沉积压差对Ga₂O₃薄膜结晶质量的影响。结果表明,Ga₂O₃在425~650 ℃温度区间存在物相转换关系。随着沉积温度从425 ℃升高至650 ℃,薄膜结晶分别由非晶态、纯α-Ga₂O₃结晶状态向α-Ga₂O₃、β-Ga₂O₃两相混合结晶状态改变。通过原子力显微镜表征探究了生长温度对Ga₂O₃薄膜表面形貌的影响,从475 ℃升高至650 ℃时,薄膜表面粗糙度由26.8 nm下降至24.8 nm。同时,高分辨X射线衍射仪测试表明475 ℃、5 Pa压差条件下的α-Ga₂O₃薄膜样品半峰全宽仅为190.8″,为高度结晶态的单晶α-Ga₂O₃薄膜材料。     

Influence of the mixed alkali effect on the chemical durability of Na2O---TiO2---SiO2 glasses

The influence of the mixed alkali effect on the chemical durability of Na₂O---TiO₂---SiO₂ glasses during substitution of K₂O for Na₂O in 21Na₂O---26TiO₂---53SiO₂ glasses was investigated. The best chemical durability was found at K₂O/Na₂O = 2.5 where the minimum was close to K⁺ ions of larger size. It was shown that the water corrosion process of the system was predominantly controlled by both the mobility and the exchange function of K⁺ ions resulting in the generation of a titanium-rich and silicon-rich layer at the surface. The mixed alkali effect can therefore be applied to lower the rate of water corrosion and increase chemical durability so that optical glasses with higher chemical durability can be obtained.     

射频磁控溅射氧气流量对制备的Ga2O3∶Cr薄膜光致发光性能的影响

在不同氧气流量下,采用双靶射频磁控共溅射的方法在蓝宝石(α-Al₂O₃)基底上制备得到系列掺Cr的Ga₂O₃(Ga₂O₃∶Cr)薄膜,详细研究了薄膜在900 ℃退火前后的结构和光学性能。结果表明,未退火的Ga₂O₃∶Cr薄膜为非晶结构,其发光主要位于蓝绿波段。经900 ℃退火后,薄膜的结构由非晶变为多晶,且在近红外波段观测到了来源于Cr³⁺掺杂的发光。退火后的薄膜结晶质量和近红外发光均与氧气流量密切相关,而其光学带隙不受氧气流量的影响。在所研究的氧气流量范围,4 mL/min氧气流量下薄膜的近红外发光强度最强,这与此条件下薄膜结晶质量较好以及Cr³⁺替代Ga³⁺的数量较多有关。以上研究成果可为制备高质量Ga₂O₃∶Cr薄膜提供参考。     

Structural analysis of anodic alumina films

Structures of amorphous anodic alumina films have been investigated by the X-ray radial distrubution function and the correlation method. The amorphous anodic alumina films are considered to contain AlO₅ coordination polyhedra as well as AlO₄ tetrahedra and AlO₆ octahedra. Two types of conformation are taken into account by the correlation method; one (model A) is the conformation in which the above coordination polyhedra are arranged in a similar way to that found in the crystalline modifications of γ-Al₂O₃ within a short range of r < 4.5 Å and the other (model B) is the conformation in which coordination polyhedra are randomly arranged. The final model formed by mixing these two conformations (model A and B) in 1 : 1 ratio describes quantitatively the observed scattering intensity curves of the amorphous anodic alumina films.     

Structural distribution and rigidity of the glass network determined by EPR of Cu

The linewidth-broadening of the EPR spectra of Cu²⁺ in silicate, borate and phosphate glasses was analyzed in terms of the distribution of g_| and A_| (δ_| and δA_|) and related to the distribution of the rigidity of the network structure. X- and K-band spectra were measured for the glasses doped with ⁶³Cu²⁺ (93% abundance). The linewidth of the HFS shoulders with parallel orientation to H increased linearly with increasing m or microwave frequency. δg_| and δA_| showed a marked dependence on glass composition. For example, in Na₂O---B₂O₃ glasses, on going from x (mol% of Na₂O) being small through intermediate to large, δg_| varied from small through large to negligibly small. In contrast to these glasses δg_| was extremely large for 75PbO · 25B₂O₃ glass. The large δg_| for the Na₂O---B₂O₃ glassesof intermediate x was attributed to the coexistence of various borate groups competitively coordinating to Cu²⁺. Negligibly small δg_| for 70Na₂O · 30B₂O₃ glass and extremely large δg_| for 75PbO ·25B₂O₃ glass, both with a narrower structural distribution, reflect regidity of the glass network. The Pb---O bonding is strong enough to distort the coordination of Cu²⁺-complex. The situation is the reverse in Na₂O---B₂O₃ glasses.     

Effect of heat treatment on phase transformation of aluminum nitride ultrafine powder prepared by chemical vapor deposition

Ultrafine aluminum nitride (AlN) powders were obtained by chemical vapor deposition via AlCl₃–NH₃–N₂ system operated at various temperatures and at a same 200 cm³/min flow rate of NH₃ and N₂, respectively. It has been shown that when the reaction temperature of AlCl₃ and NH₃ was above 600°C, then crystalline AlN powder can be formed; whereas, amorphous AlN was obtained with NH₄Cl if reacted in a lower-temperature zone of the reaction chamber. The amorphous AlN powder was heat treated at 1400°C under NH₃ and N₂ atmosphere for 2 h, then the crystalline phases of the obtained powder belong to a single phase of AlN; a mixture of AlN and Al₂O₃ and only AlON, respectively. On the other hand, if crystalline AlN powder is heat treated at 1400°C under N₂ atmosphere for 2 h, the crystalline phases were composed of the major phase of AlN and a minor phase of Al₂O₃. The morphology, particle size and agglomerate size of the AlN powder were strongly dependent on the heat-treatment temperature. The particle size of AlN powder increases from 28.1 to 45.0 nm, as the heat treatment temperature increases from 800 to 1400°C.