Doping Modification Of SCNN-based Ceramics

Sr2-xCaxNaNb5O1（5SCNN）ceramics with filled tungsten bronze structure have beenconsidered as a new photorefractive material because of high Curie temperature(Tc=270°C),high piezoelectric coefficients (d33=270pC/N) and electrooptic coefficient(r33=1325×10-12m/V，r51=1100×10-12m/V) This thesis address on the cracking ofcrystal during the preparation of SCNN-based ceramics, doping BFO,La2O3andchanging sintering technology, to investigate the effects on the sintering process,crystal structure, dielectric properties of SCNN-based ceramics through doping andchanging sintering technology.xBiFeO3(BFO)-(1-x)SCNN ceramics were prepared by solid state reaction methodand the effects of BFO on sintering behaviors, crystal structure, dielectric properties ofSCNN ceramics were investigated. Orthorhombic tungsten bronze phase were formedin the prepared SCNN ceramics and the dielectric constant and dielectric loss wereε=904.2, tanδ=0.04(10kHz) at room temperature. Sintering behaviors of SCNNceramics were improved. The sintering temperatures decreased to1275°C with dopingBFO and the cracking of crystal during the preparation of SCNN-based ceramics werecontrolled, the dielectric constant and dielectric loss were ε=936.8, tanδ=0.03(10kHz)at room temperature. The dielectric constant increased rapidly with the increasing ofBFO and the dielectric loss first increased slightly then sharply increased.La2O3doped SCNN-based ceramics were prepared by solid state reactionmethod.The effects of La2O3on sintering behaviors, crystal structure, dielectricproperties of SCNN ceramics were investigated. Tetragonal tungsten bronze phasewere formed in the prepared La2O3doped SCNN–based ceramics. The bestdielectrical properties of SCNN–based ceramics were obtained with doping0.5%（w/w%）La2O3and the dielectric constant and dielectric loss were ε=1499.3, tan δ=0.03(10kHz) at room temperature. Two phase transitions were observed between-50°C and360℃respectively correspond to the ferroelectric/ferroelastic phasetransition (Tm=0℃) and paraelectric/ferroelectric phase transition（Tc=260℃）.Thedielectric peak were broadened which show the SCNN-based ceramics exhibited typicalbut less pronounced characteristics of relaxation. La2O3doped SCNN-based ceramics were prepared by solid state reaction methodand the effects of sintering process oncrystal structure, dielectric properties of SCNNceramics were investigated. The best dielectrical properties of SCNN–based ceramicswere obtained with doping0.5%（w/w%）La2O3sintered at the condition of warmingup to1350℃then holding at1250℃for6hours. The dielectric constant and dielectricloss were ε=1488.3, tan δ=0.04(10Hz) at room temperature. Two phase transitionswere observed between-50°C and360°C, which respectively correspond to theferroelectric/ferroelastic phase transition and paraelectric/ferroelectric phase transition.The roadening dielectric peaks show the SCNN-based ceramics exhibited a typicalcharacteristic of relaxation and show stronger dielectric relaxor and dispersionfrequency.