Theoretical Study Of Phase Transitions And Multicaloric Effect In Ba(Zr_xTi_1-x)O₃ Under Multi-fields

Ba(ZrxTi1-x)O3 solid solutions can be used to manufacture microwave resonator,piezoelectric transducers,infrared detector and ferroelectric random access memories due to their excellent dielectric,piezoelectric,pyroelectric and ferroelectric properties.The electric and mechanical fields have a substantial impact on the phase transitions and physical properties in Ba(ZrxTi1-x)O3 solid solutions.In this paper,the phase transition,dielectric and piezoelectric properties under electric and mechanical fields in Ba(ZrxTi1-x)O3(x=0,x=0.1,x=0.2)solid solutions are investigated using Landau-Ginzburg-Devonshire thermodynamic approach.We also investigate the electrocaloric effect,elastocaloric effect,barocaloric effect and mulitcaloric effect in materials using the phenomenological theory.The main contents and results are given as follow.1.The monoclinic MA?MB and Mc phases are induced by fields along the[011]and[111]direction in BaTiO3,which has a cyclic phase change and the rhombohedral phase occurs twice as well as the orthorhombic phase.Meanwhile,?22 and d33 are significantly improved during the phase transition.However,there is no cyclic phase change for Ba(Zr0.iTi0.9)O3 and Ba(Zr0.2Ti0.8)O3.The monoclinic phases of the three component materials are induced by uniaxial tensile stress,and the tetragonal phase of the materials is enlarged by tensile stress.Meanwhile,it is obvious that the curie temperature of the three component materials have been increased by tensile stress.There is no monoclinic phases of the three component materials induced by hydrostatic pressure.Furthemore,the dielectric and piezoelectric properties of the three component materials have not been significantly improved under hydrostatic pressure.2.Three component materials have great adiabatic temperature changes under the electric field and mechanical field.At E=10MV/m,negative electrocaloric effect have been found for fields along the[001]and[011]direction in BaTiO3.But a normal electrocaloric effect exists for field along[111]direction and electrocaloric adiabatic temperature change is 2.6K near room temperature.When the temperature is around 350K,the barocaloric effect of Ba(Zr0.iTi0.9)O3 reaches about 4.7K under the hydrostatic pressure of 1.5GPa.With the increase of uniaxial tensile stress,the adiabatic temperature changes of the three component materials are increased,but the strength of the elastocaloric effect are decreased gradually.The adiabatic temperature changes of the three component materials near room temperature are also significantly improved under the hydrostatic pressure,which plays a significant role in the solid-state refrigeration technology.3.The multicaloric adiabatic temperature change of BaTiO3 under both uniaxial tensile stress of 200MPa and electric field E=10MV/m along the[011]direction is 3.6 K near the ferroelectric-paramectic phase transition temperature and the temperature span is increased to about 150K.The multicaloric adiabatic temperature change of BaTiO3 is about 4.5K near room temperature under both hydrostatic pressure of 1.5GPa and electric field E=10MV/m along the[111]direction,while the adiabatic temperature change of Ba(Zr0.iTi0.9)O3 material is about 5.2K near 350K.Compared with the single caloric effect,the adiabatic temperature changes of the three component materials have been greatly improved under the collective effect of multiple fields,and the temperature span of the materials have been greatly expanded near room temperature.Therefore,the multicaloric effects of Ba(ZrxTi1-x)O3 solid solutions can be improved by multi-fields,which is very important for improving cooling performance.