Cold sintering process(CSP) provides an effective method for controlling grain size through lowtemperature densification in hundreds of ceramic materials,including ZnO-based ceramics.However,the interfacial layers,res...Cold sintering process(CSP) provides an effective method for controlling grain size through lowtemperature densification in hundreds of ceramic materials,including ZnO-based ceramics.However,the interfacial layers,residual amorphous phases,and insufficient ionic solubility left by CSP hinder the overall performance of cold-sintered ZnO varistor ceramics.Here,thermal treatment is employed to assist cold-sintered ZnO varistor ceramics in addressing the defects arising from the CSP.Using CSP at 300 ℃,large-size ZnO varistor samples(40 mm in diameter) with a relative density(ρ_(r)) of ~90%were achieved.Following the thermal treatment,the amorphous phase(e.g.,Bi_(2)O_(3),Y_(2)O_(3),and Co_(2)O_(3)) was transformed into Bi-rich phases,which effectively filled pores and bonded loose grains,resulting in a notable increase in ρ_(r) to ~98% and an impressive Vickers hardness of 252 HV.Meanwhile,the interfacial layer surrounding the ZnO grains transformed into high-resistance grain boundaries that are essential for high nonlinear ohmic properties.Specifically,the sample annealed at 850 ℃exhibited a high Schottky barrier(Φ_(B)) of 0.97 eV and an ultra-low leakage current of 2.1 μA cm^(-2),leading to a remarkable breakdown electric field(Eb) of 1573 V mm^(-1) and a high nonlinear coefficient(α) of 96.This work thus shows that combining CSP and thermal treatment provides a significant guideline for designing ZnO varistor ceramics with superior mechanical and electrical performances.展开更多
基金financially supported by the National Natural Science Foundation of China(No.U23B20115)the Fok Ying-Tong Education Foundation,China(No.171050)
文摘Cold sintering process(CSP) provides an effective method for controlling grain size through lowtemperature densification in hundreds of ceramic materials,including ZnO-based ceramics.However,the interfacial layers,residual amorphous phases,and insufficient ionic solubility left by CSP hinder the overall performance of cold-sintered ZnO varistor ceramics.Here,thermal treatment is employed to assist cold-sintered ZnO varistor ceramics in addressing the defects arising from the CSP.Using CSP at 300 ℃,large-size ZnO varistor samples(40 mm in diameter) with a relative density(ρ_(r)) of ~90%were achieved.Following the thermal treatment,the amorphous phase(e.g.,Bi_(2)O_(3),Y_(2)O_(3),and Co_(2)O_(3)) was transformed into Bi-rich phases,which effectively filled pores and bonded loose grains,resulting in a notable increase in ρ_(r) to ~98% and an impressive Vickers hardness of 252 HV.Meanwhile,the interfacial layer surrounding the ZnO grains transformed into high-resistance grain boundaries that are essential for high nonlinear ohmic properties.Specifically,the sample annealed at 850 ℃exhibited a high Schottky barrier(Φ_(B)) of 0.97 eV and an ultra-low leakage current of 2.1 μA cm^(-2),leading to a remarkable breakdown electric field(Eb) of 1573 V mm^(-1) and a high nonlinear coefficient(α) of 96.This work thus shows that combining CSP and thermal treatment provides a significant guideline for designing ZnO varistor ceramics with superior mechanical and electrical performances.
