Growth of lithium doped silver niobate single crystals and their piezoelectric properties

Lithium doped silver niobate (Ag_1−xLi_xNbO₃, 0 < x < 0.1) is one of the candidate materials for lead-free piezoelectric materials. In this study, Ag_1−xLi_xNbO₃ single crystals were successfully grown by a slow cooling method. Crystal structure was assigned to perovskite-type orthorhombic (monoclinic) phase. Dielectric properties were measured as a function of temperature. As a result, with increasing lithium contents, the phase transition at around 60 °C was shifted to lower temperature while the phase transition at around 400 °C was shifted to higher temperature. On the basis of these peak shifts, the lithium contents in Ag_1−xLi_xNbO₃ single crystals were determined. Moreover, P–E hysteresis measurement revealed that pure silver niobate crystal was weak ferroelectrics with P_r of 0.095 μC/cm² while Ag_0.9Li_0.1NbO₃ (ALN10) crystal was normal ferroelectrics with P_r of 10.68 μC/cm². About this ALN10 crystal, polling treatment was performed and finally piezoelectric properties were measured. As a result, high electromechanical coupling coefficient k₃₁ over 70% was observed.     

Domain patterns on ferroelectric Rh:BaTiO3 single crystals

Single crystal growth and domain structure of Rh:Barium titanate (BaTiO₃) have been investigated. Rh doping in BaTiO₃ is effective for the growth of bulk crystals without twin formation. Atomic force microscope (AFM) and optical microscope studies reveal the formation 180° and 90° domains on the grown crystals. It has been observed that the complex 180° domain structure with typical size of around 20 μm exists in the c-domain of {0 0 1} face of Rh doped BaTiO₃ crystals.     

Microtube-Czochralski (μT-CZ) growth of bulk benzophenone single crystal for nonlinear optical applications

Microtube-Czochralski technique was employed to grow large size benzophenone single crystal for the first time. In conventional Czochralski pulling technique, the growth of bulk single crystal will be initiated by a pre-grown seed, whereas in microtube-Czochralski technique a microtube that is made out of a metal such as stainless steel (8 μm ID) can be used to grow bulk single crystal. A specially designed furnace having inert gas atmosphere, condensation free enclosure and in situ annealing facility was employed. Benzophenone crystal having cubic facet (15 mm) with high optical quality was grown when the following vital growth parameters are set to the corresponding optimized values such as pulling rate: 1–2 mm/h, seed rotation rate: 5–10 rpm and the axial thermal gradient: 8 °C/cm. The grown crystals were cut and polished. Thin plate like polished samples were used to justify the optical quality of the grown samples by UV–VIS–NIR spectroscopy. Powder SHG measurement shows that the grown samples exhibit three times higher second harmonic generation than potassium dihydrogen phosphate (KDP).     

Low cycle fatigue behaviour of a plasma-sprayed coating material

Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma-sprayed coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a larger programme to understand the fatigue behaviour coated single crystals, fully reversed, total-strain controlled fatigue tests were run on a ‘free standing’ NiCoCrAiY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650°C, where the NiCoCrAiY alloy has modest ductility, and at 1050°C, where it is extremely ductile, showing tensile elongation in excess of 100%. At the lower test temperature, deformation-induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two-phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, [001]-oriented PWA 1480 single crystals at 1050°C, but at 650°C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.     

Crystal data and indirect optical transitions in Tl2InGaSe4 crystals

The room temperature crystal data and the optical properties of the Bridgman method grown Tl₂InGaSe₄ crystals are reported and discussed. The X-ray diffraction technique has revealed that Tl₂InGaSe₄ is a single phase crystal of monoclinic structure. The unit cell lattice parameters, which were recalculated from the X-ray data, are found to be a = 0.77244 nm, b = 0.64945 nm, c = 0.92205 nm and β = 95.03°. The temperature dependence of the optical band gap of Tl₂InGaSe₄ single crystal in the temperature region of 290–500 K has also been investigated. The absorption coefficient was calculated from the transmittance and reflectance data in the incident photon energy range of 1.60–2.10 eV. The absorption edge is observed to shift toward lower energy values as temperature increases. The fundamental absorption edge corresponds to indirect allowed transition energy gap of 1.86 eV that exhibited a temperature coefficient γ = −3.53 × 10⁻⁴ eV/K.     

Temperature effects of PTFE diffusers

Poly(tetrafluoroethylene) (PTFE) is the most commonly used diffuser material in ultraviolet irradiance measurements. The temperature sensitivities of five PTFE diffusers were measured over a broad temperature range. The transmittance change varied from −0.015%/°C to −0.1%/°C. At 19 °C there was an unexpected abrupt change in transmittance ranging from 1% to 3%. This change is due to the change of the crystal structure of PTFE at 19 °C. Temperature sensitivity decreases significantly the accuracy of high precision measurements, especially if the temperature of the diffusers is not stabilized.     

Synthesis, growth and thermal and Fourier transform infrared spectral characterization of tetraethylammonium tetrachloro manganate (II) monohydrate crystals

Single crystals of a novel tetraethylammonium tetrachloro manganate (II) monohydrate (TEATC-Mn) were grown by slow evaporation solution technique at room temperature. These crystals belong to a class of interesting ferroelectric materials. The grown crystals were characterized through powder X-ray diffraction (XRD), thermogravimetry, differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC) studies and Fourier transform infrared (FTIR) spectra. While the results of the elemental analysis of the compound agree with the stoichiometry, its crystallinity is confirmed by the powder X-ray diffraction pattern. The weight losses observed were suitably explained based on the formulated decomposition pattern. The differential thermal analysis of the compound conforms to the thermogravimetric study. The endothermic peak observed in the high temperature differential scanning calorimetry suggests the occurrence of a phase transition in the compound between 300 and 370 °C while the corresponding low temperature study shows thermal anomalies at −41.7, −51.7 and at −52.4 °C. This suggests the occurrence of both first and second order phase transitions. The characteristic absorptions in the FTIR spectrum further characterize the compound. Further investigations on the ferroelectric behaviour of the compound at low temperatures are in progress.     

Internal friction associated with phase transformation of nanograined bulk Fe–25 at.% Ni alloy

The internal friction and modulus of a nanograined bulk Fe–25 at.% Ni prepared by an inert gas condensation and in situ warm consolidation technique were measured in temperature range −100 to 400 °C by means of a dynamic mechanical analyzer (DMA). An internal friction peak at around −75 °C associated with martensitic transformation was observed. During heating, an internal friction peak at about 200 °C accompanied with the decrease of modulus was also observed, which was proved by XRD that this may mainly be attributed to the reverse phase transformation of stress-induced martensite (SIM). Some abnormal features of modulus versus temperature were observed and discussed.     

Crystal growth and optical properties of CdS-doped lead silicate glass

The crystal growth and optical properties of CdS microcrystallite-doped lead silicate glass is investigated in this paper. The existence of CdS nanocrystals was confirmed via X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results reveal that a two-stage heat-treat procedure can produce a better size distribution of CdS nanocrystals than a one-stage heat-treat procedure in glasses. The second harmonic generation (SHG) from the base glass and CdS microcrystallite doped glasses was observed, and the effects of the heat treatments and the thermal poling temperature on the crystallization of CdS and second-order harmonic (SH) intensity were discussed, respectively. It is indicated that samples doped with CdS microcrystallite showed larger SH intensity than that of the base glass. Use of a higher thermal poling temperature than the glass transformation temperature does not result in a good SH intensity in glasses.     

Effect of negatively charged species on the growth behavior of silicon films in hot wire chemical vapor deposition

The deposition behavior of silicon in hot wire chemical vapor deposition was investigated, focusing on the generation of negatively charged species in the gas phase using a gas mixture of 20% SiH₄ and 80% H₂ at a 450 °C substrate temperature under a working pressure of 66.7 Pa. A negative current of 6–21 µA/cm² was measured on the substrate at all processing conditions, and its absolute value increased with increasing wire temperature in the range of 1400 °C–1900 °C. The surface roughness of the films deposited on the silicon wafers increased with increasing wire temperature in the range of 1510 °C–1800 °C. The film growth rate on the positively biased substrates (+ 100 V, + 200 V) was higher than that on the neutral (0 V) and negatively biased substrates (− 100 V, − 200 V, − 300 V). These results indicate that the negatively charged species are generated in the gas phase and contribute to deposition. The surface roughness evolved during deposition was attributed to the electrostatic interaction between these negatively charged species and the negatively charged growing surface.     

Pyroelectric properties of BST/PLT composite thick films with addition of xPbO–(1 − x)B2O3 glass

The Ba_xSr_1−xTiO₃ (BST)/Pb_1−xLa_xTiO₃ (PLT) composite thick films (20 μm) with 12 mol% amount of xPbO–(1 − x)B₂O₃ glass additives (x = 0.2, 0.35, 0.5, 0.65 and 0.8) have been prepared by screen-printing the paste onto the alumina substrates with silver bottom electrode. X-ray diffraction (XRD), scanning electron microscope (SEM) and an impedance analyzer and an electrometer were used to analyze the phase structures, morphologies and dielectric and pyroelectric properties of the composite thick films, respectively. The wetting and infiltration of the liquid phase on the particles results in the densification of the composite thick films sintered at 750 °C. Nice porous structure formed in the composite thick films with xPbO–(1 − x)B₂O₃ glass as the PbO content (x) is 0.5 ≥ x ≥ 0.35, while dense structure formed in these thick films as the PbO content (x) is 0.8 ≥ x ≥ 0.65. The volatilization of the PbO in PLT and the interdiffusion between the PLT and the glass lead to the reduction of the c-axis of the PLT phase. The operating temperature range of our composite thick films is 0–200 °C. At room temperature (20 °C), the BST/PLT composite thick films with 0.35PbO–0.65B₂O₃ glass additives provided low heat capacity and good pyroelectric figure-of-merit because of their porous structure. The pyroelectric coefficient and figure-of-merit F_D are 364 μC/(m² K) and 14.3 μPa^−1/2, respectively. These good pyroelectric properties as well as being able to produce low-cost devices make this kind of thick films a promising candidate for high-performance pyroelectric applications.     

Effect of β-spodumene on the phase development in an alumina/aluminium-titanate system

The effect of β-spodumene additions on the in situ phase formation and abundances in an Al₂O₃–Al₂TiO₅ system in the temperature range 1000–1400 °C has been studied by neutron diffraction and differential thermal analysis. Results show that β-spodumene began to decompose by phase separation and partial melting at 1290 °C, followed by complete melting at 1330 °C. Formation of Al₂TiO₅ was observed to occur at 1310 °C and its abundance increased with temperature. The addition of β-spodumene as a sintering aid did not cause its reaction with alumina or rutile to form additional phases. Addition of β-spodumene in excess of 5 wt% resulted in pronounced vitrification, which partly recrystallised when cooled to room temperature. The temperatures of Al₂TiO₅ formation and melting of β-spodumene are consistent with the results of differential thermal analysis.     

Glass-free LTCC microwave dielectric ceramics

The sintering behavior, microstructure and microwave dielectric properties of complex pyrophosphate compounds AMP₂O₇ (A = Ca, Sr; M = Zn, Cu) were investigated in this paper. All compounds could be densified below the temperature of 950 °C without any glass addition, and exhibit low permittivity (_r < 8), high Q × f value and negative temperature coefficient of resonant frequency. The Q × f value was discussed from the point of view of bond strength. The chemical compatibility with silver and copper was also investigated. All compounds seriously react with silver at 700 °C. However SrZnP₂O₇ could be co-fired with copper in reduced atmosphere. The microwave dielectric properties of SrZnP₂O₇ sintered at 950 °C in reducing atmosphere are: _r = 7.06, Q × f = 52781 GHz, τ_f = −70 ppm/°C. In terms of its lower sintering temperature, chemical compatibility with copper and good microwave dielectric properties, SrZnP₂O₇ ceramic is very promising for low temperature co-fired ceramic (LTCC) applications.     

Ageing behavior of a Cu-bearing ultrahigh strength steel

On ageing at different temperatures a various combination of properties has been obtained for this Cu-bearing ultrahigh strength steel. A substantial increase in strength has been obtained at 450 °C, accompanied by a drop in percentage elongation, percentage reduction in area and toughness. At 550 °C temperature extensive -Cu precipitates have been observed. The increased strength value retained in the temperature range of 450–600 °C and a secondary hardening peak obtained at 600 °C is probably due to the formation of fine Mo carbide precipitates. The decrease in strength at 650 °C along with an increase in percentage elongation, percentage reduction in area and toughness is due to the coarsening of Cu particles and a partial recovery of matrix. At 700 °C most of the Cu precipitates become rod shaped and formation of fresh martensite with a dark contrast is observed at the lath boundaries.     

Second-order non-linear optical studies on CdS microcrystallite doped lead silicate glasses

Second-order non-linear optical effect of CdS microcrystallite doped lead silicate glass is investigated in this paper. The second harmonic generation (SHG) from the base glass and CdS microcrystallite doped glasses were observed, and the effects of the heat treatments and the thermal poling temperature on the crystallization of CdS and second-order harmonic (SH) intensity were discussed, respectively. It is indicated that samples doped with CdS microcrystallite showed larger SH intensity than that of the base glass. Longer heat treatment time, higher heat treatment temperature and thermal poling temperature cannot get a good SH intensity in glasses.     

Physical models for cleavage fracture at various temperatures—Bases for local approach to fracture of HSLA steel

The author proposes the critical events controlling cleavage at various temperatures: at a very low temperature (−196 °C), critical event is the nucleation of a crack in ferrite at the precrack tip. At a moderate low temperature (around −100 °C), the critical event is the propagation of a carbide crack into the ferrite grain. With increasing temperature (around DBTT −80 °C), the carbide crack eligible to propagate into the ferrite grain should be the one initiated by a critical strain higher than that to initiate a carbide crack at low temperatures. The higher critical strain increases the flow stress by work hardening for making up the effect of lowering yield stress. At a higher temperature (−30 °C) after the crack tip is blunted to more than 60 μm and a fibrous crack extends, the critical event for cleavage fracture is the propagation of a grain-sized crack.     

Photoluminescence properties of the Yb:Er co-doped Al2O3 thin film fabricated by microwave ECR plasma source enhanced RF magnetron sputtering

The Yb:Er co-doped Al₂O₃ thin film was deposited on oxidized silicon wafers by microwave ECR plasma source enhanced RF magnetron sputtering, and annealed from 800 °C to 1000 °C. The photoluminescence at 1.53 μm of thin film was obtained under room temperature. The mixture phase structure of γ and θ is observed by XRD, and the compositions of the thin film are investigated by EPMA. The maximum PL intensity was achieved with O₂:Ar at 1:1, annealing temperature at 900 °C, and experimental ratio of Yb:Er at 1:3.6. The energy transfer mechanism between Er and Yb ions is supported by theoretical analysis and experiment results.     

Time resolved luminescence of quartz from Nigeria

Characteristics of luminescence lifetimes and luminescence intensity obtained from time resolved spectra of quartz from Nigeria are presented. The luminescence was pulse-stimulated at 11 μs width at 470 nm. Samples used consisted of unannealed quartz as well as samples annealed at 500 °C, 600 °C, 700 °C, 800 °C and 900 °C. The luminescence lifetimes and luminescence intensities were studied as a function of annealing temperature, irradiation dose and measurement temperature. It was found that there is a decrease, although non-monotonic, in the luminescence lifetime with change in annealing temperature from 20 to 900 °C. In addition, lifetimes extracted from time resolved spectra of unannealed samples as well as ones annealed at 500 °C and 600 °C are initially independent of irradiation dose but do later decrease with further irradiation. Regarding the luminescence intensity it was observed that in general, the intensity passes through a peak as the measurement temperature is increased from 20 to 200 °C with slight differences in the detailed pattern dependent on preheating. Activation energies for thermal quenching and thermal assistance evaluated from temperature-dependent changes of luminescence lifetime and luminescence intensity are given. The results are discussed in terms of a model consisting of three luminescence centres with probability of hole trapping during irradiation being highest for the luminescence centre associated with the least lifetime.     

Influence of crystal orientation on ECAP of aluminum single crystals

A single crystal of high purity aluminum, oriented with the {1 1 1} slip plane and the 1 1 0 slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and the shear direction, was processed by equal-channel angular pressing (ECAP) through a single pass. This configuration was designated the 20° orientation and the results are compared with earlier data obtained on a similar high purity aluminum single crystal in the 0° orientation with the (1 1 1) slip plane and the 1 1 0 slip direction lying parallel to the shear plane and the shear direction. The results show that in both orientations the long axes of the subgrains lie parallel to the slip traces of the primary slip system and the average subgrain widths are 1.3 μm. However, the shearing characteristics are different because the 0° specimen exhibited a conventional B-type rolling texture whereas the 20° specimen deformed by slip on the primary slip system and this system rotated by 40° in a counter-clockwise sense as the specimen passed through the shear zone of the ECAP die.     

Influence of substrate temperature on atomic layer growth and properties of HfO2 thin films

Atomic layer growth of hafnium dioxide from HfCl₄ and H₂O has been studied at substrate temperatures ranging from 180–600°C. A quartz crystal microbalance was used for the real-time investigation of deposition kinetics and processes affecting the growth rate. It was shown that the layer-by-layer growth was self-limited at temperatures above 180°C. The data of ex situ measurements revealed that the structure, density and optical properties of the films depended on the growth temperature. The absorption coefficient of amorphous films grown at 225°C was below 40 mm⁻¹ in the spectral range of 260–850 nm. The refractive index of the films grown at 225°C was 2.2 and 2.0 at 260 and 580 nm, respectively. The polycrystalline films with monoclinic structure grown at 500°C had about 5% higher refractive index but more than an order of magnitude higher optical losses caused by light absorption and/or scattering.