Study Of B-site Doped Modification And Fabrication Of Oriented Ceramics Of Bismuth Based Layer-structured Perovskite Materials

Multiferroic materials which contains two or more of the primary ferric orderings,such as ferroelectricity,ferromagnetism and ferroelasticity have great significance in practical applications in sensors,actuators,multiple state memory elements,etc.Bismuth layer structure ferroelectrics?BLSFs?,with fatigue-free nature and ferroelectricity order,is one of the typical single-phase multiferroic materials.However,the material has a drawback of weak magnetic and weak magnetoelectric effect at low temperature.Doping magnetic elements such as Co,Fe,Cr,Mn is one of common choices to improve the performance of BLSFs.Ni is an important ferromagnetic element as well,but fewer reports about Ni substitution in m=4 BLSFs.In this research,we synthesized Bi₄NdTi₃Fe_1-xNi_xO₁₅?BNTF-Ni_x?samples by multicalcination procedure.Concluding that sample Bi₄NdTi₃Fe0.7Ni_0.3O₁₅(BNTF-Ni_0.3)exhibited best room temperature multiferroic properties.Grain-oriented BLSFs ceramics have anisotropic properties due to the structure of BLSFs have significant differences along a/b axis and c axis.In order to study the dependence of the microstructures,magnetic,dielectric properties on the crystal orientation,we prepared highly c axis oriented sample BNTF-Ni_0.3.Bi₄NdTi₃FeO₁₅?BNTF?are considered as inserting magnetic unit BFO into ferroelectric Bi₄Ti₃O12?BTO?.This paper also presents that Fe partly substituted for Ti in BTO to obtain magnetic,and synthesized the samples Bi3.15Nd0.85Ti2.4Fe_0.6O₁₅?BNT-FeO.6?with highly c-axis orientation at the same time.In this paper,BNTF ceramics doping with Ni were fabricated by multicalcination procedure.Four-layered BNTF-Ni_0.3 and three-layered BNT-Fe_0.6 ceramics were fabricated by molten salt method.And characterize the microstructure,morphology,ferroelectric,ferromagnetic and magnetoelectric coupling effect on the above samples.Some main conclusions in the dissertation are listed in the following:1.The randomly oriented Bi₄NdTi₃Fe_1-xNi_xO₁₅ ceramics prepared by multicalcination procedure:With the increase of Ni doping amount,the value of residual magnetization 2Mr and residual polarization value 2Pr increase firstly and then decrease,reached maximum at x = 0.3 and 0.5 respectively.?r reached maximum 416 in 1 MHz.Considering the ferroelectric and magnetic properties,the sample Bi₄NdTi₃Fe_1-xNi_xO₁₅?x=0.3?ceramics prepared by multicalcination procedure has the best performance.2.The c-axis and off-c-axis oriented BNTF-Ni_0.3 ceramics was synthesized by the molten salt method:XRD and SEM patterns of BNTF-Ni_0.3 ceramics clearly demonstrates that polycrystalline ceramics are strongly textured.The alignment of the particles induced by the press application remains even in the green compacts.At pre-sintering temperatures of 700-850?,orientation degree increases with pre-sintering temperature.The orientation degree of green compacts is the important factor for grain orientation.The higher the orientation degree of the green compact,the higher the orientation degree of the ceramic get,the more easily the orientation degree of the ceramic be conttolled.We studied the anisotropic magnetic,magnetodielectric properties of the surfaces?cut from the original pellet perpendicular to the pressing axis?and the section?cut from the original pellet parallel to the pressing axis?of BNTF-Ni_0.3 ceramics.There is clear evidence that the characteristic parameters of magnetic hysteresis loops,residual magnetization 2Mr,coercive field 2Hc,2Ms are strongly dependent on ??the angle between the magnetic field and the ceramic plane?.The ratio of permittivity of the sections to the surfaces direction is found to be 4 at 1 kHz.Remarkably,a clearly identified positive magnetocapacitance?MC?effect and positive magnetic loss?ML?effect was observed in the surfers?c-axis?while negative in the sections?off-c-axis?at 100 kHz.3.The c-axis and off-c-axis oriented BNT-Fe_0.6 ceramics was sprepared by the molten salt method:XRD and SEM patterns of BNT-Fe_0.6 ceramics clearly demonstrates that polycrystalline ceramics are strongly textured.When the proportion of molten salts and oxides in the range of 0.5-4,orientation degree decreases with the proportion increase.The magnetic hysteresis loops of the surfaces detect while B direction in plane??=0°?to out of plane??=90°?reveal anisotropic dielectric properties of BNT-Fe_0.6 ceramics.The ML effect and the MC effect along c-axis or off-c-axis of BNT-Fe_0.6 was similar to BNTF-Ni_0.3...