Ferroelectric thin films with giant room-temperature electrocaloric effect (ECE) could be very useful in design of solid-state refrigeration devices. Here, lead-free Ba 0.85 Ca 0.15-x Sr x Zr 0.1 Ti 0.9 O 3 (BCZT-xSr, 0.01 ≤ x ≤ 0.10) thin films are successfully prepared on the substrates (Pt/Ti/SiO 2 /Si) via sol-gel route, and the effect of the Sr substitution on the structure, electric properties and ECE of the films were investigated. The dielectric analyses show that the rhombohedral-tetragonal phase transition temperature (T R-T ) move to a higher temperature and the tetragonal-cubic phase transition temperature (T m ) shift to a lower temperature with increasing Sr content, and finally the T R-T peaks merge into the T m peaks at room temperature. The BCZT-0.05Sr film presents a giant ECE with ΔT = 27.1 K and ΔS = 30.6 J K −1 kg −1 at 800 kV cm -1 near room temperature (301 K). The giant ΔT benefits from a multiphase coexisting region with successive R-T and T-C phase transition character near room temperature. These results indicate that the lead-free Sr-doped BCZT thin film is an attractive material for application in ECE refrigeration devices.
The main inorganic minerals in natural bones are non-stoichiometric hydroxyapatite (HA, Ca 10 [PO 4 ] 6 [OH] 2 ) doped with various trace elements, which may possess important biochemical effects. To investigate the functions of Sr and Si elements in human hard tissues, non-doped HA, trace Si doped HA, Si and Sr codoped HA with the concentration of natural bones are synthesized by hydrothermal method in this study. The samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The biological activities are evaluated via cytotoxicity study, adhesion and proliferation of osteoblast measurement, and alkaline phosphatase (ALP) assay. All the synthesized materials are HA phase, which have hierarchical structures with oriented HA nanorods assembled into the platy particles. These materials are non-cytotoxic against L929 cells line even at 400 μg/ml powder suspension. The results clearly indicate that the proliferation of L929 cells increases with trace elements doping from trace Si-HA to Si + Sr-HA. The adhesion and proliferation of osteoblast measurement illustrates that proliferation of osteoblasts advances about 1.3 times for Si-HA and about 1.8 times for Si + Sr-HA compared with undoped HA. In general, Si-HA with trace Si element shows enhanced cell differentiation, and Si + Sr-HA dual-doped with Si and Sr elements presents increased biological activity compared with Si-HA.
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