Low Temperature Synthesis Of (Ag_1/4Nb_3/4)_0.01Ti_0.99O _{By Sol Seed Method 2}Research On The Dielectric Properties Of Powders And Ceramics

Dielectric materials with colossal permittivity are the key materials of multilayer ceramic capacitor(MLCC)and dynamic random access memory(DRAM),and improving their dielectric properties are the hot research topics in ceramic capacitors.In 2013,Liu et al.in Australia,realized high dielectric permittivity,low loss and good temperature stability by donor and acceptor(Nb,In)co-doped method in TiO2-based dielectric ceramics,which has aroused a lot of attention from scholars at home and abroad.Since the report,scholars have prepared a series of co-doped TiO2-based ceramic materials with different donor and acceptor ions using a traditional solid-state method and obtained colossal permittivity.However,the dielectric properties of the prepared ceramics are not comparable to that of(Nb,In)co-doped TiO2 materials reported by Liu et al.Besides,it should be noticed that the precursor powders of co-doped TiO2-based ceramics require high temperature to synthesize by the traditional solid-state method,which lead to low activity of rutile type raw materials,uncontrollable composition uniformity and high reaction temperature,and do not conducive to energy saving and consumption reduction.Therefore,it is a worth project to improve the prepared method of anatase and rutile phase TiO2-based precursor powders at low temperature and effectively enhance the dielectric properties of ceramics.This paper explored the synthesis of anatase type(A-type)and rutile type(R-tupe)(Ag1/4Nb3/4)0.01Ti0.99O2(ANTO0.01)precursor powders by the improved sol-gel method(sol-seed method)at low-temperature,and obtained high activity,uniform size and controlled chemical composition precursor powders of ANTO0.01 ceramics by optimizing the prepared process conditions.On this basis,the A-type and R-type ANTO0.01 ceramics were successfully prepared to improve the dielectric properties,and explored the origin and mechanism of colossal permittivity,the main results were as following;1.A-type ANTO0.01 precursor powders with uniform microstructure,high activity and controllable chemical components were successfully prepared by sol-seed method.Optimal prepared parameters:solution Ti concentration(CTi)is 0.4 mol/L;pH is 4.5;and calcined temperature of powders is 600?.The size of the A-type ANTO0.01 precursor powders is?12 nm and it is up to 60%of A-type structures will be transformed into R-type structures when the calcined temperature of the powder increased to 800?,while there is no tendency to transform to R-type for the A-type ANTO0.01 precursor powders were synthesized by the conventional solid-state method when the calcined temperature up to 800 ?,and the grain size of the powder did not change obviously with temperature increasing.The particle size is not uniform and poor stoichiometric ratio.Compared with the traditional solid-state method,the powders synthesized by the sol-seed method have high activity,uniform size and controllable stoichiometric ratio.The results indicated that the sol-seed method is more beneficial to synthesize A-type ANTO0.01 precursor powder.2.A-type ANTO0.01 ceramics with good dielectric properties were successfully prepared by the sol-seed method and the traditional solid-state method.The results were as following:the sintering temperature of ceramics is 1300?;the holding time is 10 h.The dielectric constant?151862 and the dielectric loss?0.208 at 1 kHz.However,the preparation of A-type ANTO0.01 ceramics by the traditional solid-state method requires a higher sintering temperature of 1330?,which is not conducive to energy saving and environmental protection,and the dielectric constant?39481 and the dielectric loss?0.245 at 1 kHz.The dielectric constant of ceramic prepared by sol-seed method is more than 3 times higher than that by the traditional solid-state method,and the dielectric loss can be kept lower,which discovers that the sol-seed method is more beneficial to obtain high performance dielectric materials with colossal permittivity.3.R-type ANTO0.01 precursor powders were synthesized successfully by the sol-seed method at low temperature.Also,R-type ANTO0.01 ceramic materials were prepared.The R-type powders with the highest synthesis degree were determined by combining the three strong peaks of the XRD and the optimal ceramic microstructure and dielectric properties.The optimal processes are solution pH:4.30,[H2O]/[Ti]:6.20,water-bath temperature:45?,CTi:0.4 mol/L,sintering temperature:1340?,holding time:10 h,and ceramics with uniform grain size were obtained.At room temperature,R-type ANTO0.01 ceramic displays excellent dielectric properties(dielectric constant?43271,dielectric loss?0.048,1 kHz)and good frequency stability(40 Hz-105 Hz).Compared with R-type ANTO0.01 ceramic prepared by the traditional solid-state method,the ceramics prepared by sol-seed method display higher dielectric constant,which further confirms that the sol-seed method is more beneficial to improve the dielectric properties in dielectric ceramic materials with colossal permittivity.4.The giant dielectric mechanism of R-type ANT0.01 ceramic with high dielectric constant and low dielectric loss is revealed.The result indicated that the phase transition(A?R-type)causes rearrangements of Ti atom,O atom and other atoms places and the number changes of[TiO6]octahedral,and affects the defect clusters concentration of ceramics at high temperature sintering,which is not conducive to the high performances of co-doped TiO2 dielectric ceramics.Meanwhile,combined with the XPS analysis of elemental valence,the giant dielectric properties of R-type ANT0.01 ceramics are attributed to the "electron pinning defect dipole(EPDD)".