Comparison of (K0.5Na0.5)NbO3 Single Crystals Grown by Seed-Free and Seeded Solid-State Single Crystal Growth.

(K0.5Na0.5)NbO3-based piezoelectric ceramics are of interest as a lead-free replacement for Pb(Zr,Ti)O3. In recent years, single crystals of (K0.5Na0.5)NbO3 with improved properties have been grown by the seed-free solid-state crystal growth method, in which the base composition is doped with a specific amount of donor dopant, inducing a few grains to grow abnormally large and form single crystals. Our laboratory experienced difficulty obtaining repeatable single crystal growth using this method. To try and overcome this problem, single crystals of 0.985(K0.5Na0.5)NbO3-0.015Ba1.05Nb0.77O3 and 0.985(K0.5Na0.5)NbO3-0.015Ba(Cu0.13Nb0.66)O3 were grown both by seed-free solid-state crystal growth and by seeded solid-state crystal growth using [001] and [110]-oriented KTaO3 seed crystals. X-ray diffraction was carried out on the bulk samples to confirm that single-crystal growth had taken place. Scanning electron microscopy was used to study sample microstructure. Chemical analysis was carried out using electron-probe microanalysis. The single crystal growth behaviour is explained using the mixed control mechanism of grain growth. Single crystals of (K0.5Na0.5)NbO3 could be grown by both seed-free and seeded solid-state crystal growth. Use of Ba(Cu0.13Nb0.66)O3 allowed a significant reduction in porosity in the single crystals. For both compositions, single crystal growth on [001]-oriented KTaO3 seed crystals was more extensive than previously reported in the literature. Large (~8 mm) and relatively dense (<8% porosity) single crystals of 0.985(K0.5Na0.5)NbO3-0.015Ba(Cu0.13Nb0.66)O3 can be grown using a [001]-oriented KTaO3 seed crystal. However, the problem of repeatable single crystal growth remains.

Two-Step Sintering of Partially Stabilized Zirconia for Applications in Ceramic Crowns.

Partially-stabilized zirconia is used in ceramic crowns due to its excellent mechanical properties and bio-inertness but does not match the natural color and translucency of tooth enamel. To reduce scattering of light and improve translucency, the grain size of zirconia ceramics should be less than the wavelength of visible light (0.4-0.7 µm), and porosity should be eliminated. The aim of the present work was to study the effect of two-step sintering of a commercial powder (Zpex Smile, Tosoh Corp., Tokyo, Japan) on the grain size and translucency of zirconia for use in ceramic crowns. Samples were sintered at a first step temperature (T1) of 1300, 1375 and 1400 °C for 5 min, followed by a decrease to the second step temperature (T2) and holding at T2 for 5-20 h. Samples were also conventionally sintered at 1450 °C for 2 h for comparison. Two-step sintered samples with an almost equal density, smaller grain size and narrower grain size distribution compared to conventionally sintered samples could be sintered. However, the translucency of two-step sintered samples had lower values compared to conventionally sintered samples. This is due to the slightly higher porosity in the two-step sintered samples. Density and translucency of both conventionally and two-step sintered samples could be increased further by using a ball milled powder.

Grain Growth Behavior of 0.95(Na0.5Bi0.5)TiO3-0.05BaTiO3 Controlled by Grain Shape and Second Phase.

The grain growth behavior of 0.95(Na0.5Bi0.5)TiO3-0.05BaTiO3 (mole fraction, NBT-5BTdid not appear in any of the NBT-5BT samples with excess Bi2O3. The amount of liquid phase increased as the amount of Bi2O3 increased. Therefore, the rate of grain growth could be decreased by the increasing the distance for the diffusion of atoms. These observations allowed us to conclude that the growth of Bi2O3-excess NBT-5BT grains is governed by the growth of facet planes via the two-dimensional nucleation grain growth mechanism during changing grain shape and amount of liquid.

Effect of Composition on the Growth of Single Crystals of (1-x)(Na1/2Bi1/2)TiO3-xSrTiO3 by Solid State Crystal Growth.

The (1-x)(Na1/2Bi1/2)TiO3-xSrTiO3 (NBT-100xST) system is a possible lead-free candidate for actuator applications because of its excellent strain vs. electric field behaviour. Use of single crystals instead of polycrystalline ceramics may lead to further improvement in piezoelectric properties but work on single crystal growth in this system is limited. In particular, the effect of composition on single crystal growth has yet to be studied. In this work, single crystals of (NBT-100xST) with x = 0.00, 0.05, 0.10 and 0.20 were grown using the method of Solid State Crystal Growth. [001]-oriented SrTiO3 single crystal seeds were embedded in (NBT-100xST) ceramic powder, which was then pressed to form pellets and sintered at 1200 °C for 5 min-50 h. Single crystal growth rate, matrix grain growth rate and sample microstructure were examined using scanning and transmission electron microscopy. The results indicate that the highest single crystal growth rate was obtained at x = 0.20. The mixed control theory of grain growth is used to explain the single crystal and matrix grain growth behaviour.

Effect of the volume fraction of zirconia suspensions on the microstructure and physical properties of products produced by additive manufacturing.

OBJECTIVE: The objectives of the present study were: (1) to analyze the dispersion and optical properties of suspensions with various volume fractions of zirconia, and (2) to assess the influence of zirconia volume fraction on the microstructure and physical properties of products produced by the additive manufacturing and sintering process. METHODS: Zirconia specimens were fabricated by an additive manufacturing technique using a DLP (digital light processing) system. The zirconia suspensions were divided into six groups based on zirconia volume fraction within the range of 48-58vol%. RESULTS: The maximum volume fraction of zirconia in suspensions possible for printing was 58vol%. The cure depth of the zirconia suspensions decreased as the volume fraction increased. The cure depth was greater than 100µm after 15s photocuring in all groups. Geometrical overgrowth tended to increase gradually as the volume fraction of zirconia increased within the range of 28.55-36.94%. The 3-point bending strength of the specimens increased as the volume fraction of zirconia in the suspension increased, reaching a maximum value of 674.74±32.35MPa for a volume fraction of 58vol%. Cracks were observed on the surfaces of zirconia specimens and these cracks increased in number as zirconia volume fraction decreased. SIGNIFICANCE: In this experiment, the viscosity of zirconia suspensions sharply increased from a volume fraction of 54vol%. Because of the very high viscosity, 58vol% was the maximum volume fraction possible for additive manufacturing. After polymerization, all specimens showed some distortion due to geometrical overgrowth. The maximum 3-point bending strength was 674.74±32.35MPa for a volume fraction of 58vol%. But the maximum strength of sintered zirconia prepared by additive manufacturing is inferior to that of conventionally sintered zirconia.

Shear Bond Strength of Zirconia to Titanium Implant Using Glass Bonding.

This study evaluated the shear bond strength of zirconia to titanium implant components using silica-based glasses and compared the strength with that of implant components bonded using a commercial resin cement. Forty cylindrical zirconia specimens and forty titanium disks (Grade IV) were divided equally into four groups, depending on the adhesive used: three different types of glasses (group G, group GI, group GIB) and a self-adhesive resin cement (group U200), which was used as a control. The shear bond strength was evaluated using a universal testing machine and failure mode was examined by optical microscope. Data was analyzed using One-way ANOVA with p-value <0.05, which was considered statistically significant. The shear bond strength of the three glass groups was significantly higher than that of group U200 (p<0.05). Failure mode in all groups was a combination of adhesive and cohesive modes. Shear bond strength of zirconia to titanium bonded using glasses was higher than that using self-adhesive resin cement.

Prostate Cancer Cell-Specific Cytotoxicity of Sub-Micron Potassium Niobate Powder.

Oxide nanoparticles have numerous potential applications in medicine such as carriers for therapeutic drugs, contrast agents for bio-imaging and targeting agents for tumors. Oxide nanoparticles may also have an inherent cytotoxicity towards cancer cells, as recently found for cerium oxide. KNbO3 nanoparticles have a combination of low toxicity and nonlinear optical properties which make them attractive for use as a bio-imaging material. However, little is known yet about the cytotoxicity of KNbO3 particles towards cancerous cells. In the present work, the cytotoxicity of KNbO3 particles to normal and prostate cancer cell lines is studied. The mixed oxide method is used to prepare KNbO3 powder. Using dynamic light scattering the mean particle diameter of the KNbO3 powder is found to be ∼500 nm. X-ray diffraction, Fourier transform infra-red spectroscopy and Raman scattering spectroscopy are used to examine the structure of the KNbO3 powder. Powder morphology is examined using scanning electron microscopy. MTT assays of EA.hy926, PC-3 and DU-145 cell lines are carried out to study cell-specific cytotoxicity. KNbO3 sub-micron particles are found to have low toxicity to PC-3 cells, moderate toxicity to EA.hy926 cells and high toxicity to DU-145 cells. A new avenue towards the treatment of prostate cancer may be opened by the cell-specific cytotoxicity of KNbO3.

Analysis of Removal Torque of Injection Molded Zirconia Implants; An Experimental Study on Beagles.

This study compared the removal torque between injection molded zirconia implants and titanium implants with resorbable blast media (RBM) surfaces in beagle humeri. Fifteen screw-shaped implants were classified into 3 groups; titanium implant with RBM surface (Group RT), injection molded zirconia implant (Group Zr) and injection molded zirconia implant with sand-blasted surface (Group ZrS). Implants were inserted into beagle humeri. After 12 weeks, removal torque values were measured. The Zr group has a slightly higher removal torque value than the RT and ZrS groups but there were no significant differences among groups. Zirconia implants shows a similar removal torque to RBM titanium implants. This in vivo study showed injection molded zirconia implants could be an alternative to RBM titanium implants in terms of removal torque.

Simple synthesis of highly catalytic carbon-free MnCo2O4@Ni as an oxygen electrode for rechargeable Li-O2 batteries with long-term stability.

An effective integrated design with a free standing and carbon-free architecture of spinel MnCo2O4 oxide prepared using facile and cost effective hydrothermal method as the oxygen electrode for the Li-O2 battery, is introduced to avoid the parasitic reactions of carbon and binder with discharge products and reaction intermediates, respectively. The highly porous structure of the electrode allows the electrolyte and oxygen to diffuse effectively into the catalytically active sites and hence improve the cell performance. The amorphous Li2O2 will then precipitate and decompose on the surface of free-standing catalyst nanorods. Electrochemical examination demonstrates that the free-standing electrode without carbon support gives the highest specific capacity and the minimum capacity fading among the rechargeable Li-O2 batteries tested. The Li-O2 cell has demonstrated a cyclability of 119 cycles while maintaining a moderate specific capacity of 1000 mAh g(-1). Furthermore, the synergistic effect of the fast kinetics of electron transport provided by the free-standing structure and the high electro-catalytic activity of the spinel oxide enables excellent performance of the oxygen electrode for Li-O2 cells.

Sintering of Lead-Free Piezoelectric Sodium Potassium Niobate Ceramics.

The potassium sodium niobate, K0.5Na0.5NbO3, solid solution (KNN) is considered as one of the most promising, environment-friendly, lead-free candidates to replace highly efficient, lead-based piezoelectrics. Since the first reports of KNN, it has been recognized that obtaining phase-pure materials with a high density and a uniform, fine-grained microstructure is a major challenge. For this reason the present paper reviews the different methods for consolidating KNN ceramics. The difficulties involved in the solid-state synthesis of KNN powder, i.e., obtaining phase purity, the stoichiometry of the perovskite phase, and the chemical homogeneity, are discussed. The solid-state sintering of stoichiometric KNN is characterized by poor densification and an extremely narrow sintering-temperature range, which is close to the solidus temperature. A study of the initial sintering stage revealed that coarsening of the microstructure without densification contributes to a reduction of the driving force for sintering. The influences of the (K + Na)/Nb molar ratio, the presence of a liquid phase, chemical modifications (doping, complex solid solutions) and different atmospheres (i.e., defect chemistry) on the sintering are discussed. Special sintering techniques, such as pressure-assisted sintering and spark-plasma sintering, can be effective methods for enhancing the density of KNN ceramics. The sintering behavior of KNN is compared to that of a representative piezoelectric lead zirconate titanate (PZT).

The Effect of Niobium Doping on the Electrical Properties of 0.4(Bi0.5K0.5)TiO3-0.6BiFeO3 Lead-Free Piezoelectric Ceramics.

Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1-xNbxO3-0.6BiFe1-xNbxO3 (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d33 meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d33 and Smax/Emax.

Effect of transition metal dopants on mechanical properties and biocompatibility of zirconia ceramics.

In this study, the effect of transition metal dopants, originally added as colouring agents, on the mechanical properties and biocompatibility of sintered zirconia was investigated. This study confirmed that transition metal dopants could have a slight detrimental effect on the mechanical properties of zirconia. The addition of metal dopants did not affect the adhesion and proliferation of gingival fibroblasts.