Structure,Dielectric And Ferroelectric Characteristics Of Filled Tungsten Bronze Ceramics With Oxygen-Defficiency

In thisartical,It is mainly discussed that effects of oxygen-dificiency on crystal structure,dielectric and ferroelectric properties in filled of niobate.Recently,it is more popular to explor the structure and properties of tetragonal tungsten bronzes.While,the most of the research is about the effects of A-site to oxygen octahedron,which is the origin of the structure and properties of tetragonal tungsten bronzes.Nowadays,oxygen deficiencies has been induced by atomophere or.This article induces oxygen deficiencies by stoichiometric ratio contro to research the effects of oxygen deficiencies on tetragonal tungsten bronzes' structure and properties.Oxygen-deficient tungsten bronze ceramics with general formula Sr5SmTi3+2xNb7-2xO30-x(x=0,0.1,0.25)are prepared.The effects of oxygen deficiency on the crystal structure,dielectric and ferroelectric properties are investigated.With increasing oxygen deficiency,the crystal structure becomesless stable and the lattice shrinks,while the ferroelectricity is weakened,and the low temperature relaxation enhanced.Commensurate superlatticeis observed in Sr5SmTi3Nb7O30,corresponding to the onset of the ferroelectric transition as reported previously.In compositions with x=0.1 and 0.25,two factors that A-site cross occupancies and disturbance of oxygen vacancieson the ferroelectric order are noticed and related to the change from ferroelectric behavior to diffuse one.Three orders of incommensurate superlattice reflections are observed in x=0.1 and 0.25 compositions.The first-order incommensurate superlattice reflections appear at positions(h+1/4-d,k+1/4-d,l+1/2),reflecting the common feature in tungsten bronzes with relaxor or diffuse ferroelectric nature.The second-order incommensurate superlattice reflectionsare observed on the(00k)(k=0,1,2,3...)planes around the(h+1/2,k+1/2,l)positions,while the third-order incommensurate superlattice reflections are observed on the(00k)(k=1/2,3/2,...)planes,by the side of the first-· order ones.The appearance of higher-order is believedto reducethe high structural energyinduced by the oxygen deficiency.Tungsten Bronzes Sr4Sm2Ti4+2xNb6-2xO30-x with Oxygen-Deficiency is successfully synthesized by standard solid-state reaction.With the increasing of x,the ferroelectricity and structure stability are weaken,while relaxor,permittivity and temperature-stability are enhanced.For x=0.25,the permittivity was promoted to around 200(around 100 for x=0 and 0.1)at board temperature.The dielectric loss is 0.0255 at room temperature 1MHz,and below 0.02 over 339K.Besides,the permittivity deviation below 15%is from 207K to more than 573K,only 3.5%from269K to 566K.At last,it may be a new way to find temperature stability dielectrics by introducing oxygen deficiencies.