Thermal and Mechanical Properties of Lithium Borate Glasses in Relation to the Glass Structure

In lithium borate glasses RLi₂OB₂O₃ (0R<0.4), the following experimental results were obtained: 1. The density increases monotonically with increasing R. 2. Both velocities of longitudinal and transverse ultrasonic waves increase monotonically with increasing R. 3. The elastic constants such as bulk modulus and Young's modulus increase monotonically with increasing R. 4. The linear expansion coefficient shows a broad minimum at around R=0.25. 5. The Poisson ratio shows a minimum at around R=0.10 and a maximum at around R=0.20. 6. Each of the temperature coefficients of velocities for longitudinal and transverse ultrasonic waves shows a sharp minimum at R=0.10 and a sharp change in slope at R=0.20. The experimental results 1, 2 and 3 can be ascribed to a change in short-range order groups. The experimental result 4 is ascribable to the most compact configuration at around R=0.25. The experimental results 5 and 6 are ascribable to a change in crosslink between six-membered borate rings.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nanoporous Glass as a Model System for a Consistency Check of the Different Techniques of Diffusion Measurement

The remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of a hierarchy of transport resistances in addition to the diffusional resistance of the pore system and their differing influence due to the differing diffusion path lengths covered by the different measuring techniques. We report diffusion measurements with nanoporous glasses where the existence of such resistances could be avoided. Molecular propagation over diffusion path lengths from hundreds of nanometers up to millimeters was thus found to be controlled by a uniform mechanism, appearing in coinciding results of microscopic and macroscopic diffusion measurement.     

Er3+/Yb3+共掺杂铋酸盐玻璃的上转换发光和能量传递

用高温熔融法制备了Er³⁺/Yb³⁺共掺杂的45Bi₂O₃-45GeO₂-10PbO玻璃,对玻璃样品进行了光谱测试,分析了上转换发光机制和Yb³⁺→Er³⁺的能量传递效率。通过Yb³⁺离子浓度对Er³⁺离子在铋酸盐玻璃中的上转换荧光强度影响的研究,得到Er³⁺质量分数为0.5%以及Yb³⁺质量分数为2.5%时上转换发光强度最大。研究结果表明,在970nm泵浦激发下,Er³⁺/Yb³⁺共掺杂B₄₅G₄₅P₁₀玻璃在532,545,673nm处产生较强的上转换绿光和红光,是一种较为理想的上转换发光基质材料。     

Dual self-organised shear banding behaviours and enhanced ductility in phase separating Zr-based bulk metallic glasses

The multiplication and interaction of self-organised shear bands often transform to a stick-slip behaviour of a major shear band along the primary shear plane, and ultimately the major shear band becomes runaway and terminates the plasticity of bulk metallic glasses (BMGs). Here, we examined the deformation behaviours of the nanoscale phase-separating Zr_65–xCu₂₅Al₁₀Fe_x (x = 5 and 7.5 at.%) BMGs. The formation of multi-step phase separation, being mainly governed by nucleation and growth, results in the microstructural inhomogeneity on a wide range of length-scales and leads to obviously macroscopic and repeatable ductility. The good deformability can be attributed to two mechanisms for stabilizing shear banding process, i.e. the mutual interaction of multiple shear bands away from the major shear band and the delaying slip-to-failure of dense fine shear bands around the major shear band, both of which show a self-organised criticality yet with different power-law exponents. The two mechanisms could come into effect in the intermediate (stable) and later plastic deformation regime, respectively. Our findings provide a possibility to enhance the shear banding stability over the whole plastic deformation through a proper design of microstructure heterogeneities.     

Physical,optical and radiative properties of CaSO4–B2O3–P2O5 glasses doped with Sm3+ ions

Trivalent rare earth ions doped borosulfophosphate glasses are in high demand owing to their several unique attributes that are advantageous for applications in diverse photonic devices. Thus, Sm³⁺ ion doped calcium sulfoborophosphate glasses with composition of 25CaSO₄–30B₂O₃–(45?x)P₂O₅–xSm₂O₃ (where x?=?0.1, 0.3, 0.5, 0.7 and 1.0 mol%) were synthesized using melt-quenching technique. X-ray diffraction confirmed the amorphous nature of the prepared glass samples. Differential thermal analyses show transition peaks for melting temperature, glass transition and crystallization temperature. The glass stability is found in the range 91?°C to 116?°C which shows increased stability with addition of Sm₂O₃ concentration. The Fourier transform infrared spectral measurements carried out showed the presence of vibration bands due to PO linkage, BO_3, BO₄, PO₄, POP, OPO, SOB, and BOB unit. Glass density showed increase in value from 2.179 to 2.251?g cm^?3 with increase in Sm₂O₃ concentration. The direct, indirect band gap and Urbach energy calculated were found to be within 4.368–4.184?eV, 3.641–3.488?eV and 0.323–0.282?eV energy ranges, respectively. The absorption spectra revealed ten prominent peaks centered at 365, 400, 471, 941, 1075, 1228, 1375, 1477, 1528 and 1597?nm corresponding to ⁴D_3/2,⁶H_5/2→⁴I_11/2,⁶P_3/2, ⁶F_11/2, ⁶F_9/2, ⁶F_7/2, ⁶F_5/2, ⁶F_3/2, ⁶H_15/2 and ⁶F_1/2 transitions respectively. Photoluminescence spectra monitored at the excitation of 398?nm exhibits four emission bands positioned at 559, 596,643 and 709?nm corresponding to ⁴G_5/2→⁶H_5/2, ⁶H_7/2, ⁶H_9/2 and ⁶H_11/2 transitions respectively. The nephelauxetic parameters calculated showed good influence on the local environment within the samarium ions site and the state of the SmO bond. The Judd–Ofelt intensity parameters calculated for all glass samples revealed that Ω_6?>?Ω_4?>?Ω₂. The emission cross-section and the branching ratios values obtained for ⁴G_5/2→⁶H_7/2 transition indicate its suitability for LEDs and solid-state laser application.     

高温金属熔体黏度突变探索

高温金属熔体的黏度是衡量液态金属动力学性质的一个重要指标,是高温金属熔体的基本物理性能之一.熔体的黏度在表征脆性系数、金属玻璃形成能力的大小和液-液相变现象方面起关键性作用.本文在介绍高温金属熔体黏度测量方法的基础上,综合评述了单质、二元和多元合金黏度随温度的变化规律和黏度突变特征,分析了黏度突变研究的物理意义,并指出高温金属熔体黏度今后研究的发展方向。     

亚碲酸铅玻璃微结构的Raman光谱研究

测定了亚碲酸铅玻璃的常温及高温Raman光谱。实验表明随着PbO浓度增大,亚碲酸盐玻璃中的四配位与三配位结构单元之间存在转化关系,体系总体非桥氧数增加。当加入的PbO摩尔浓度增大至50%后,四配位结构单元密度相对较少,这时玻璃结构中主要以三配位结构单元形式存在。同时还测定了40PbO·60TeO2玻璃的升温Raman光谱,观察到四配位结构单元桥氧、四配位结构单元非桥氧以及三配位结构单元非桥氧对称伸缩振动的谱峰由于温度升高引起的结晶化过程导致向高频移动,谱峰变得尖锐,强度增大。熔点后,Raman光谱出现展宽效应,强度降低。在玻璃处于熔化状态下,四配位中的微结构单元会进一步向三配位转化,熔体内部微结构单元含量会相对平衡。     

Crystallization kinetics and Avrami index of Sb-doped Se–Te–Sn chalcogenide glasses

Bulk amorphous samples of Sb-substituted Se_78?xTe₂₀Sn₂Sb_x (0 < x < 6) have been prepared using melt quench technique. The structure of Se_78?xTe₂₀Sn₂Sb_x (x = 0, 2, 4, 6) glassy alloys has been investigated using X-ray diffraction technique. Calorimetric studies of the prepared samples have been performed under non-isothermal conditions using differential scanning calorimetry (DSC) and glass transition temperature as well as crystallization temperature has been evaluated using DSC scans. The activation energy of crystallization kinetics (E_c) has been determined using model-free approaches such as Kissinger, Ozawa, Tang and Starink methods. The Avrami index (n) and frequency factor (K_o) have been calculated by Matusita and Augis–Benett method.     

Study of aluminium-modified Ge2Sb2Te5 thin films for the applicability as phase-change storage device material

Electrical and optical studies have been carried out on aluminium-modified Ge₂Sb₂Te₅ thin films to check its applicability as an active material in optical and electrical memory storage devices. Five polycrystalline bulk samples were prepared with compositions: Al_x(Ge₂Sb₂Te₅)_1?x; x = 0, 0.08, 0.14, 0.21, 0.25. Amorphous thin films were deposited from the polycrystalline bulk by thermal evaporation. Temperature-dependent resistance shows the increase in crystallization temperature of Ge–Sb–Te films on aluminium addition. Activation energy for conduction, conductivity, optical band gap, coefficient of refraction and extinction coefficient are studied with respect to Al content in both amorphous and crystalline phases of Ge–Sb–Te alloy films.