Research On Template-free Solid-state Growth And Microstructure Of Alkali Metal Niobate Micronanomaterials

There are many kinds of alkali metal niobate,such as perovskite structural alkali metal niobate?K,Na?Nb O₃ material with excellent piezoelectric and ferroelectric properties,and square tungsten bronze structural alkali niobate?Na,K?₆Nb_10.6O₃₀ which has excellent photocatalytic properties.In the same system,nanostructured materials often have unique properties and potential applications.At present,there is no report on artificial preparation of super-long nanowires by solid state method.This paper mainly studied the preparation and structure of?Na,K?₆Nb_10.6O₃₀ micro/nanowire by a templating-free solid-state method,and explored the possibility of preparing?K,Na?Nb O₃ micro/nanowire materials by the same method,and then by the way studied the structure and properties of the?K,Na?Nb O₃ materials with different nano-structures found during the process of exploration.Main research results are as follows.The super-long?Na,K?₆Nb_10.6O₃₀-based micro/nanowires with square tungsten bronze structure were prepared by the template-free solid-state method.The micro/nanowires grew directly from ceramic matrix without introducing external impurities.The micro/nanowire cluster is composed of many single nanowires,which has a strip texture along its growth direction.There is an obvious boundary between the root of the nanowire and the ceramic substrate,which is a transition zone within the boundary.The transition zone is amorphous,and the nanowires are single crystalline,which crystalline orientation is???.The ceramic matrix has a perovskite crystalline structure and the micro/nanowires have a square tungsten bronze crystalline structure.The elements contents in both the ceramic and nanowire crystals is different.In addition,the template-free solid-state growth mechanism of the micro/nanowires was supposed.The effect of sintering temperature,holding time and kinds of niobium resource on the growth habit and structure of?Na,K?₆Nb_10.6O₃ micro/nanowires was studied.The results show that the niobium oxalate can replace niobium pentaoxide to improve the morphology of the micro/nanowires,and reduce the pre-firing and sintering temperature and the holding time,and increase the production of the micro/nanowires.It is also possible to replace the ball-milling media,anhydrous ethanol,with ultra-pure water.When the content of niobium oxalate is 3.2%,all the powders synthesized at different pre-firing temperatures have perovskite structure,with a certain degree of lattice distortion.The sintering temperature and holding time was optimized in order to facilitate the growth of the micro/nanowires.When the sintering temperature is 1112?and the holding time is 24h,the growth of micro/nanowires is the best within the scope of this study.The growth possibility of the Mg,Mn and Bi co-doped Na_0.5K_0.5Nb O₃ and La,Ba and Bi co-doped K_0.54Na_0.46Nb O₃ micro/nanowires by explored.Although the two kinds of micro/nanowires expected were not grew by the same method,other forms of nano-structural materials were obtained and then studied.Studies show that Mg O doping can be helpful for the growth of Na_0.5K_0.5Nb O₃-based crystals with nanodomains.When the doping content is 0.5,the single crystal size is the largest.The dielectric loss of Mg O-doped single crystal is relatively low.When the doping content is 0.6%,the piezoelectric coefficient d₃₃ of the crystal is 203 p C/N,the residual polarization Pr is37.4?C/cm²,the coercive electric field Ec is only 7 k V/cm.The addition of La is beneficial to the preparation of K_0.54Na_0.46Nb O₃-based nanocrystalline transparent ceramics.Both the density and transmittance?55%?of transparent ceramics are the highest when the doping content is 1.5%.The reasons on the formation of the alkali metal niobate with different nanostructure were discussed.