Enhanced electrocaloric effect at room temperature in Mn^(2+) doped lead-free(BaSr)TiO_(3) ceramics via a direct measurement

(Ba_(1-x)Sr_(x))(MnyTi1-y)O_(3)(BSMT)ceramics with x=35,40 mol%and y=0,0.1,0.2,0.3,0.4,0.5 mol%were prepared using a conventional solid-state reaction approach.The dielectric and ferroelectric properties were characterized using impedance analysis and polarization-electric field(P-E)hysteresis loop measurements,respectively.The adiabatic temperature drop was directly measured using a thermocouple when the applied electric field was removed.The results indicate that high permittivity and low dielectric losses were obtained by doping 0.1-0.4 mol%of manganese ions in(BaSr)TiO_(3)(BST)specimens.A maximum electrocaloric effect(ECE)of 2.75 K in temperature change with electrocaloric strength of 0.55 K·(MV/m)^(-1)was directly obtained at~21℃and 50 kV/cm in Ba_(0.6)Sr_(0.4)Mn_(0.001)Ti_(0.999)O_(3) sample,offering a promising ECE material for practical refrigeration devices working at room temperature.

First-Principles Study on the Stability and Electronic Properties of Bi-Doped Sr_3Ti_2O_7

The electronic and crystal structural properties of Bi-doped Sr3Ti2O7 are studied using the first principles density functional theory（DFT）based on pseudopotentials basis and plane-wave method.Our results show that the formation energy of Bi doping in Site-1 and Site-2 of Sr3Ti2O7 increases with increasing doping concentration.And at the same doping concentration,the formation energy of Bi doping in Site-2 is lower than that in Site-1.The undoped Sr3Ti2O7is found to be an insulator and its Fermi level stays at the top of the valence band.While the Fermi level of the Bi-doped Sr3Ti2O7moves into the bottom of conduction band,the system undergoes an insulator-to-metal phase transition.Furthermore,our calculation results demonstrated that the Fermi level of the Bi-doped Sr3Ti2O7goes deeper into the bottom of conduction band with increasing doping concentration.