Anti-reductive Characteristics And Permittivity Stability Against Temperature Of BaAl₂O₄-based Multilayer Capacitor Ceramics

Multilayer ceramic capacitors?MLCCs?are significant electronic components widely used in the electronic industry.This paper focused on BaAl2O4-based ceramics,and successfully prepared a series of temperature stable C0 G MLCCs dielectric ceramics over ultra-wide temperature through doping modification.The exploring work has been done to fill the vacancy of temperature higher than 200 ° C and lower than –55 ° C temperature stable C0 G MLCCs.Furthermore,numerous systematic works and innovative researches have been done on the relationships among the compositions,crystal structures and ultra-wide stability of dielectric materials.[Zn_0.5Si_0.5]³⁺ was used as doped ion to completely replace the Al³⁺ in the B sites of BaAl2O4 material,and the transformation law of structure,improving sinterability and dielectric properties were studied in detail.When the doping amount was 40% total ions in the B site,the densification temperature of the system was reduced by 355 ?,and meanwhile the capacitance stability was broaden to –50 ? – 450 ?.The improvement of capacitance stability was achieved by the unique replacing mechanism in the doping process which caused the structure transition of BaAl2O4-based solid solution.Zn2+ ions and Si4+ ions were not the traditional average substitutions in the B site,but Zn2+ ions preferentially occupied Al1 and Al4 of the 6c-wyckoff site and 2b-wyckoff site,while Si4+ ions preferentially replaced Al2 and Al3 of the 6c-wyckoff site and 2b-wyckoff site.It was the unique replacing mechanism that the 2bWyckoff site Al/(Zn_0.5Si_0.5)disorder and tetrahedra distortion appeared leading to relaxor-like behavior?a second-order ferroelectric transition?,thus improving the temperature stability.The influence of partial substitution of Zn/Ti ions on dielectric properties of BaAl2O4-based ceramics was studied in depth.Appropriate amount of Zn/Ti ions could reduce densification temperature and improve capacitance stabililty of BaAl2O4-based ceramics.And the capacitance stability was broaden to –100 ? – 700 ?.[Zn_0.5/Ti_0.5]³⁺ ions occupied four different Al³⁺ ion positions averagely,and the bond length of Al1/?Zn,Ti?-O,Al2/?Zn,Ti?-O and Al3/?Zn,Ti?-O increased with the increase of x.The improvement of capacitance stability was achieved by moving the first dielectric abnormal peak from 123 ? to –22 ?.The movement of the dielectric peak attributed to the lower atomic shift amplitude ?z of B cations along the polar axis by doping.High temperature impedance spectrum and XPS analysis showed that the electron-pinned defect-dipoles in the lattice resulted in low dielectric loss,ultra-wide temperature stability and ultra-high insulation resistivity.In the air,oxygen and Zn vacancies were in an approximately equal equilibrium state.Thus,the content of holes or weakly bound electrons in the sintered body was extremely low,and the conductive loss was minimal.Its comprehensive properties were: ?r = 18.4,tan? 10-3,–27 ppm/? ? TCC ? +10 ppm/??–100 ? to 700 ??and resistivity ⁶.9×1014 ?·cm.However,the material has no anti-reducing property and cannot be co-fired with the nickel electrode.A new BaAl?2-2x?(Mg_0.5Ti_0.5)_2xO₄?x = 0.03?ceramic with an ?r value of 18.5 at room temperature and Tc significantly reduced?-25 ??and Curie peak memorably widened was prepared.The densification temperature of the system was reduced to 1260 ?.The main crystal phase was still barium aluminate,and the high performance ceramic meeting the requirements of C0 G MLCCs was prepared by peak shifting dopant.The effect of the peak shifting dopant was analyzed from the crystal structure and Curie peak movement.On the basis of crystallography theory,the introduction of peak shifting dopant caused the increase of bond lengths Al1/?Mg,Ti?-O,Al2/?Mg,Ti?-O and Al3/?Mg,Ti?-O,leading to lattice distortion.The increase of bond length decreased the displacement amplitude ?z of B site atoms along the polar axis,thus causing the Curie temperature to drop.According to the bond valence theory,the larger the bond grew,the weaker the bond energy was,which reduced the tilted restoring force of the lattice recovered oxygen tetrahedron and decreased the TCC value.The changes of resistivity in different atmospheres indicated that the dielectric ceramics exhibit p-type semiconductor behavior at high temperature,and the Ea of conductivity?2.137 e V?in N2-H2 was higher than that in air?1.500 e V?,indicating that the ceramics had excellent anti-reductive characteristics and could realize co-firing with Ni electrodes.Its comprehensive properties were: ?r = 18.5,tan? 10-3,-22 ppm/? ? TCC ? +20 ppm/??–100 ? to 700 ??and resistivity ⁴.5×1014 ?·cm.BAMT MLCCs were prepared by casting method.The BAMT MLCCs had higher crystallinity and smaller grain size than BAMT ceramics.The SEM of cross-section showed the lamination structure was clear and the interfaces between Ni electrodes and ceramic medium were good.Eventually,we have developed ultrawide stability C0 G base metal electrode?BME?MLCCs with high performance,its main performance index for: ?r = 18.7,tan? 10-3,-20 ppm/? ? TCC ? +11 ppm/??–100 ? to 700 ??,and resistivity ⁷.4×10¹⁵ ?·cm.