Synthesis,Structure And Electrical Properties Of AM(N/O)₂-type(Oxy)nitride

With the rapid development of the information industry in modern society,the requirements for electronic components become higher.High permittivity materials are the decisive factor for the storage density and device size of capacitor elements.It is important to explore the high permittivity materials in order to develop modern information industry.Now,high permittivity materials are mainly oxides.Comparing the chemical properties of N and O,people found that the polarizability of N is higher than O,which makes the(oxy)nitride have the potential to become a high dielectric permittivity material.The layered nitride CaTiN₂ reported in 2017 has a high bulk dielectric constant of 1300-2500 within 10⁴-10⁶ Hz from 80 to 450 K,but the mechanism of that is not very clear.Therefore,we want to study the composition design,multi-method preparation and the relationship between structure and dielectric properties on the basis of the formula of CaTiN₂.(1)By high temperature solid phase synthesis,a series of doping experiments of CaTiN₂ were carried out in order to explore the origin of the high bulk dielectric permittivity of CaTiN₂.Through the experiment of Sr doping of CaTiN₂,it is concluded that the high bulk dielectric permittivity of CaTiN₂ may come from the distortion of itsTiN₅ polyhedron,which provides a theoretical guidance for the further exploration of high bulk dielectric permittivity nitrides.According to this conclusion,we carried out the experiment of doping CaTiN₂ with Mg,but failed,because Mg₃N₂was volatile and could not enter the cells of CaTiN₂ at high temperature.While the raw material was inert at low temperature.Then the experiment of doping Ba to CaTiN₂ was carried out,and Ba was successfully mixed into the cell of CaTiN₂.However,due to the volatilization of Ba₃N₂,the actual amount of incorporation was seriously inconsistent with the theoretical amount(2)A new layered nitride was designed and prepared on the basis of the formula of CaTiN₂.The solid solution sample of(MgTiN₂)_x(Ti N)_y was obtained by high temperature solid phase synthesis.It has a structure similar toTiN,but its dielectric properties are not satisfaction.For the synthesis of BaTiN₂,a mixture of BaTiN₂ and Ba₂Ti N_2.6 was obtained due to the incorrect ratio of raw materials.The synthesis of Ca Zr N₂ was failed,although we tried different temperatures.Because the Ca₃N₂ is sensitive at high temperatures,which makes the reaction difficult to succeed.(3)Study the dielectric properties of known nitrides.Due to the defects and vacancies produced during the sintering process of the ceramic pellets,we cannot obtain the intrinsic properties of the sample.While we study the dielectric properties of Sr Hf N₂,we found that the permittivity of Sr Hf N₂ can reach 300-500 in 10⁴-10⁶ Hz at 5-285 K.the neutron diffraction data were refined by using the space group of R-3m reported in literature,but the result is not satisfaction.Then,the space group of R3m was used for refinement,and the result is better.So the R3m is more suitable for Sr Hf N₂,furthermore the R3m is an non-centrosymmetric space group,which may be the reason for the high dielectric constant of Sr Hf N₂.(4)A new oxynitride was designed and prepared on the basis of the formula of CaTiN₂.We tried to synthesize KTi NO by high temperature solid phase method and soft-chemistry method,but did not succeed.Because the sample is prone to form potassium titanate oxides at low temperatures,and the K is easy to volatile at high temperatures,and Ti⁴⁺is also easy to be reduced by ammonia,it is difficult to obtain the target compound.The NaTiNO was synthesized by high temperature and pressure method.We tried to synthesize the samples under different high pressure conditions of10 GPa,5 GPa and 2 GPa,and we didn't get the target compound.However we could get another new phase at the pressure condition of 2 GPa.