Boosting ultra-wide temperature dielectric stability of multilayer ceramic capacitor through tailoring the combination types of polar nanoregions

With the rapid development of space exploration and new energy vehicles,it is urgent to build ultra-wide temperature multilayer ceramic capacitors(UWT MLCCs)to match electronic circuits that can withstand harsh environmental conditions.Relaxor ferroelectrics with diffuse phase transition feature are potential dielectrics for the construction of UWT MLCCs.However,how to ensure high dielectric constant together with low dielectric loss in the wide temperature region is still a big challenge.Here,the above difficulties are addressed by tailoring the combination types of polar nanoregions(PNRs)in the(1-x)(0.8Na_(0.5)Bi_(0.5)TiO_(3)-0.2K_(0.5)Bi_(0.5)TiO_(3))-xNaTaO3(NBT-KBT-xNT)system.Compared with PNRS types of P4bm+R3c and P4bm+Pbnm,the combination type of P4bm+Pbnm+R3c PNRs in NBT-KBT-0.31NT is the most beneficial to obtain comprehensive excellent dielectric performance because it can balance the relationship between high dielectric constant and temperature stability over a wide temperature region.Further,by optimizing the laminating pressure and co-firing temperature to realize a tight interfacial structure between the dielectric layer and the Pt inner electrode,a record-high dielectric constant(er=(907%±15%))together with low dielectric loss(tan δ≤0.025)is achieved over an ultra-wide range from-61℃ to 306℃ for NBT-KBT-0.31 NT MLCC,demonstrating that tailoring the combination types of PNRs is a powerful strategy in designing UWT MLCC dielectrics.

Defect Engineering with Rational Dopants Modulation for High‑Temperature Energy Harvesting in Lead‑Free Piezoceramics

High temperature piezoelectric energy harvester(HTPEH)is an important solution to replace chemical battery to achieve independent power supply of HT wireless sensors.However,simultaneously excellent performances,including high figure of merit(FOM),insulation resistivity(ρ)and depolarization temperature(Td)are indispensable but hard to achieve in lead-free piezoceramics,especially operating at 250°C has not been reported before.Herein,well-balanced performances are achieved in BiFeO3–BaTiO3 ceramics via innovative defect engineering with respect to delicate manganese doping.Due to the synergistic effect of enhancing electrostrictive coefficient by polarization configuration optimization,regulating iron ion oxidation state by high valence manganese ion and stabilizing domain orientation by defect dipole,comprehensive excellent electrical performances(Td=340°C,ρ250°C>10^(7)Ωcm and FOM_(250°C)=4905×10^(–15)m^(2)N^(−1))are realized at the solid solubility limit of manganese ions.The HT-PEHs assembled using the rationally designed piezoceramic can allow for fast charging of commercial electrolytic capacitor at 250°C with high energy conversion efficiency(η=11.43%).These characteristics demonstrate that defect engineering tailored BF-BT can satisfy high-end HT-PEHs requirements,paving a new way in developing selfpowered wireless sensors working in HT environments.

Enhanced electrical resistivity and mechanical properties in BCTZ-based composite ceramic

Environmental and human health concerns about lead toxicity have prompted the development of lead-free piezoceramics.Among them,(Ba_(0.85)Ca_(0.15))(Zr_(0.1)Ti_(0.9))O_(3)(BCTZ)with excellent piezoelectric properties has the most potential and attracts extensive attention.However,lack of concern toward electrical resistivity and mechanical properties has greatly hindered its practical application.Here,we report the achievement of enhanced insulation characteristics(grain electrical resistivity increased by one order of magnitude)and superior mechanical properties(Vickers hardness value increased by 40%)in Al_(2)O_(3)-added BCTZ composite ceramics.Such improvement can be attributed to specific composite microstructure,where the nonferroelectric second phase dispersed in the grain interior and grain boundary of BCTZ matrix results in blocking effect on the electric current paths as well as propagation of microcracks.These findings will pave a new way for the practical application of BCTZ ceramics.

Relaxation mechanism analysis of synthetic fused quartz glass investigated by electrical impedance spectra

The synthetic fused quartz glasses with bare metal impurities have been analyzed by temperaturedependent electrical impedance spectroscopy. The complex electric impedance and the overlapping of the normalized dielectric modulus imply the single mechanism of dielectric and conduction relaxation in the fused quartz glass.Besides, the dependence of conductivity on temperature may attribute to the predominant electric relaxation to the delocalized or long range electronic hopping between the nonbridged dangling oxygen.

LOW-FIRING SOL-GEL DERIVED Mn-DOPED 0.92(K_(0.5)Na_(0.5))NbO_(3)-0.08LiNbO_(3)LEAD-FREECERAMICS WITH ENHANCED PIEZOELECTRIC PROPERTIES

Mn-doped 0.92(K_(0.5)Na_(0.5))NbO_(3)-0.08LiNbO_(3)(0.92KNN-0.08LN)lead-free piezoelectric cer-amics have been prepared by a developed sol-gel routes using Nb_(2)O_(5)as Nb source.Due to thehigh quality of gel precursor,Mn-doped 0.92KNN-0.08LN nanopowders with the mean particlesize about 20 nm were obtained at 500℃.The addition of Mn can promote the densification ofnanopowders effectively at 950℃,and also influences in a pronounced way both the crystal structure and microstructure of the materials.With the increase of the amount of Mn addition,0.92KNN-0.08LN ceramics are transformed from dominant orthorhombic to coexistence of the orthorhombic and tetragonal phases,and the grain sizes are enhanced simultaneously.Optimizedparameters,such as d_(33)=212 pC/N and k_(p)=0.46,were achieved in 0.2 Mn-doped0.92KNN-0.08LN systems,which are good candidate material for lead-free piezoelectric devices.