The Cold Sintering Praparation And Performance Of Mo-Bi Based Ceramics

Mo-Bi based?Bi₂O₃,MoO₃,Bi₂Mo O₆?ceramics are widely used in the field of wireless communication such as resonators,filters,dielectric substrates,dielectric antennas,and dielectric waveguides due to their excellent dielectric properties.With constant development of communication technology,microwave devices are required to achieve high integration,low cost and low firing.Most dielectric ceramics'sintering temperature is greater than 1000?and they cannot be co-fired with the electrode material.In order to reduce the sintering temperature of ceramics,sintering agent are usually added.However,the dielectric properties of ceramics are deteriorated by the introduction of sintering agent,so it is difficult to meet the low firing demand of LTCC.Therefore,there is an urgent need to develop a method to reduce sintering temperature of ceramics.In this paper,Mo-Bi based ceramics with high density were prepared by ultra-low temperature cold sintering,the effect of instant solvent concentration,applied pressure,sintering temperature,holding time,and sintering curve during sintering on the performance of ceramic structures was investigated.Besides,the densification mechanism of Mo-Bi based ceramics prepared by ultra-low temperature cold sintering.The specific research content and results are as follows:?i?MoO₃ ceramic with a high density was prepared using acetic acid as co-solvent,and the influence of technological parameters on ceramic sintering characteristics was studied.According to the research results that the effect of acetic acid concentration on the relative density of ceramics is significant.MoO₃ ceramic with a relative density of96.85%was prepared at 200?/250 MPa for 30 min using 2 mol/L acetic acid aqueous solution as co-solvent.In order to further increase the relative density of ceramics and reduce the sintering conditions,MoO₃ ceramic prepared using a two-stage sintering method first at 180?/200 MPa for 15 minutes and then heated to 200??200 MPa?for 15 min had a relative density of 97.90%,a grain size of 1.19?m,a dielectric constant of 10.56,a Qf of 2336 GHz.After annealing at 600?,the relative density and dielectric of the ceramics decreased to 94.12%and 9.61,respectively,the grain size and Qf increased to 2.39?m and 26000 GHz.?ii?Cold sintering technology was first applied to Bi₂O₃ ceramics.The effect of one-step and multi-step cold sintering on the structure and properties of ceramics was compared by using acetic acid solution as a co-solvent.The first stage of cold sintering was held at 270?/330 MPa for 140 min.The relative density of the ceramic reached98.31%,and its the permittivity,quality factor and grain size are 32.2,16425 GHz and4.20?m,respectively.For multi-step cold sintering,in the first step,the relative density of the Bi₂O₃ ceramic,subjected to 155?and 300 MPa for 25 min,is 96.23%.The relative density of the Bi₂O₃ ceramic increase to 98.52%,after processing at 210?and300 MPa for 25 min,in the second step.Finally,in the third stage of the processing,under the condition of holding at 270?/300 MPa for 25 minutes,which enabled the Bi₂O₃ ceramic obtain a grain size of 4.02?m,?_r of 33.44,Qf of 16218 GHz,and a relative density of 99.13%.The performance of Bi₂O₃ ceramics obtained by one-step cold sintering and multi-step cold sintering is similar to that of conventional Bi₂O₃ceramics obtained at 680?,but cold sintering can greatly reduce the sintering temperature of Bi₂O₃ ceramics.?iii?Pure phase Bi₂Mo O₆ ceramics were prepared by cold sintering using Bi₂O₃and MoO₃ as raw materials.The effects of different cosolvents on the phase and micromorphology of ceramics were explored.Suitable co-solvent can avoid the generation of heterophase and increase the density of ceramics.Bi₂Mo O₆ ceramics prepared with acetic acid solution as co-solvent had many heterophases and poor density.Pure phase Bi₂Mo O₆ ceramics with relative density of 93.13%can be prepared by using acetic acid and ammonia as co-solvent.The?_r and Qf of pure phase Bi₂Mo O₆ceramics were 25.22 and 8000 GHz,respectively.