Room-Temperature Plastic Deformation of Strontium Titanate Crystals Grown from Different Chemical Compositions
Oxide materials have the potential to exhibit superior mechanical properties in terms of high yield point, high melting point, and high chemical stability. Despite this, they are not widely used as a structural material due to their brittle nature. However, this study shows enhanced room-temperature plasticity of strontium titanate (SrTiO3) crystals through the control of the chemical composition. It is shown that the deformation behavior of SrTiO3 crystals at room temperature depends on the Sr/Ti ratio. It was found that flow stresses in deforming SrTiO3 crystals grown from a powder with the particular ratio of Sr/Ti = 1.04 are almost independent of the strain rate because of the high mobility of dislocations in such crystals. As a result, the SrTiO3 crystals can deform by dislocation slip up to a strain of more than 10%, even at a very high strain rate of 10% per second. It is thus demonstrated that SrTiO3 crystals can exhibit excellent plasticity when chemical composition in the crystal is properly controlled.
Synthesis, characterization and in vitro biocompatibility study of strontium titanate ceramic: A potential biomaterial.
Strontium (Sr), a mineral element present in trace in the human body, has significant effect on bone remodelling. Sr containing ceramics have huge potential to heal bone defects and improve osseointegration of implants. In this study, perovskite oxide - strontium titanate (SrTiO3) was synthesized and explored its potential for biomedical applications. The phase pure SrTiO3 powder was synthesized from solid state reaction of strontium carbonate (SrCO3) and titanium dioxide (TiO2) at 1200 °C for 2 h. The as synthesized SrTiO3 powder, pure hydroxyapatite (HAp) and SrTiO3-50 wt% HAp (SH50) premixed powders were sintered at different temperatures varies from 1100 to 1400 °C in air. The sintered samples were characterized using X-ray diffraction (XRD) for phases and scanning electron microscopy (SEM) for microstructure analysis. XRD results revealed no dissociation of HAp or reaction with SrTiO3 during sintering. The sintered samples were studied for mechanical properties, wettability, and biocompatibility. The relative density of the sintered SrTiO3 increases with increasing sintering temperature. The relative density of SrTiO3 was increased from 77% to 98% with increase in sintering temperature from 1250 to 1400 °C. The substantial improvement of hardness and compressive strength was observed for sintered SrTiO3 compared to HAp of similar porosity level. The hardness and compressive strength of SrTiO3 sintered at 1250 °C found ~6 and ~3.5 times higher than sintered HAp. In vitro dissolution study carried out in phosphate buffer solution at 37 °C, confirmed the release of Sr2+ ion from the bulk SrTiO3 sintered at 1250 °C. The in vitro cell materials interaction showed cytocompatibility of sintered SrTiO3 and SrTiO3-HAp composite. In summary, excellent biocompatibility of SrTiO3 with superior mechanical properties confirmed its potential as novel biomaterial for use in the repair of infected or aseptic bone defects.
Dislocation pile-ups: From {110} cracking in MgO to model strength evaluations
Abstract The researches of Professor J.C.M. Li and his colleagues and students have been involved with dislocation pile-up descriptions in a number of ways: beginning from the interpretation of microindentation experiments on MgO single crystals, then carrying over to tabulation of various pile-up characteristics including those for dislocation loops expanding against the grain boundary resistance, and, lastly, interpreting grain size dependent material strength properties. The pioneering work is related here to accumulated pile-up results and Hall–Petch type interpretations also extending downwards in scale to nanocrystalline grain size materials.