We investigated the athermal high-pressure behavior of the elastic properties of SrTiO3 (STO) up to 26 GPa in cubic, tetragonal and orthorhombic phases using the ab initio pseudo-potential method. Our results for the cubic phase are in good agreement with experiment and previous pseudo-potential calculations. There are no studies for the tetragonal and orthorhombic phases under high pressure available for comparison. To date, there are no global data on elastic parameters under high pressure for STO. We establish data when we report the results of our structural and elastic study under high pressure in the three phases. Our calculations show that the cubic–tetragonal phase transition occurs at 6 GPa and the tetragonal–orthorhombic phase transition at 14 GPa. A third and unknown phase transition from orthorhombic Cmcm to monoclinic P21 /m was observed at 24 GPa, but no study has explored it. The orthorhombic phase is unstable and this instability may be due to ferroelectricity at high pressure. The elastic properties of STO are also strongly pressure dependent with instabilities near the phase transition pressure. STO is more resistant to plastic deformation and to fracture in the cubic phase than in the tetragonal and orthorhombic phases.

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The aim of this study is to provide a remedy for the low thermophysical properties of air, which is used as a fluid of transfer in solar collectors. A fully developed flow needs to be created by the use of staggered fin rows soldered under the absorber plate. The fluid flow undergoes contractions followed by expansions, which creates a fully developed turbulent flow, and increases the thermal heat transfer between the absorber plate and the air. The fins increase the heat transfer surface, from which an appreciable improvement of the thermal heat performance of solar air heaters has been found in comparison to those of solar air heaters with a plane absorber. In this work we have tested the influence of the dimension of the fins and the influence of the space between consecutive fin rows mounted in staggered rows.