Electrical analysis of inter-growth structured Bi_4Ti_3O_(12)-Na_(0.5)Bi_(4.5)Ti_4O_(15) ceramics

Inter-growth bismuth layer-structured ferroelectrics（BLSFs）, Bi_4Ti_3O_（12）-Na_（0.5）Bi_（4.5）Ti_4O_（15）（BIT-NBT）, were successfully synthesized using the traditional solid-state reaction method. X-ray diffraction（XRD） Rietveld refinements were conducted using GSAS software. Good agreement and low residual are obtained. The XRD diffraction peaks can be well indexed into I2 cm space group. The inter-growth structure was further observed in the high-resolution TEM image. Dielectric and impedance properties were measured and systematically analyzed. At the temperature range 763-923 K（below T_c）, doubly ionized oxygen vacancies（OVs） are localized and the short-range hopping leads to the relaxation processes with an activation energy of 0.79-1.01 eV. Above T_c, the doubly charged OVs are delocalized and become free ones, which contribute to the long-range dc conduction. The reduction in relaxation species gives rise to a higher relaxation activation energy ~ 1.6 eV.

Sm and Mn co-doped PMN-PT piezoelectric ceramics:Defect engineering strategy to achieve large d_(33)and high Q_(m)

PbTiO_(3)-based piezoelectric ceramics are key materials for developing various electromechanical transduc-ers.For high-power ultrasonic transducers,piezoelectric ceramics are required to possess large piezo-electric coefficient(d_(33))and high mechanical quality factor(Q_(m)).Although acceptor dopants can im-prove Q_(m),they also deteriorate d_(33).If suitable piezoelectricity-beneficial donor dopants can be intro-duced into acceptor-doped ceramics,it is very possible to obtain large d_(33)and high Q_(m)simultaneously in donor and acceptor co-doped ceramics.In this work,a series of x mol%Sm and y mol%Mn co-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-30PbTiO_(3)(PMN-30PT:x Sm,y Mn)ceramics were prepared by the solid-phase sintered method.The crystal structure,local domain structure and electromechanical properties were sys-tematically analyzed.Optimal performances were obtained in PMN-30PT:2.5Sm,1-2Mn ceramics with d_(33)=860-543 pC/N,Q_(m)=495-754,and dielectric loss tanδ=0.0055-0.0086.This high performance origi-nates from the combined effects of(Mn″Ti−V_(o)^(••))^(×)defect dipoles and the local structural heterogeneity.

La_(2)O_(3)-modified BiYbO_(3)–Pb(Zr,Ti)O_(3) ternary piezoelectric ceramics with enhanced electrical properties and thermal depolarization temperature

High-performance Pb(Zr_(1−x)Ti_(x))O_(3)(PZT)piezoceramics are urgently desired by the market in view of their expanded operating temperature range,reduced property temperature dependence,and enhanced sensitivity and acoustic power.In this work,we reported a kind of low-cost and high-performance 0.06BiYbO_(3)–0.94Pb(Zr_(0.48)Ti_(0.52))O_(3) ternary piezoceramics;the modifying effects of La_(2)O_(3) on this perovskite system were investigated in terms of the structures,electrical properties,and thermal depolarization behaviors of ceramics.The field-dependent dielectric and conduction properties indicated that there are close correlations among oxygen vacancies(VO),conducting electrons,and intrinsic conduction process.The degradation in ferroelectric properties observed in those samples doped with more than 0.15 wt%of La_(2)O_(3) indicated that the occupying mechanisms of La^(3+)changed from the donor substitution for Pb^(2+)to the isovalent substitution for Bi^(3+).The thermally depoling micromechanisms of ceramics were revealed from the thermodynamic processes of defect dipoles and intrinsic dipoles within ferroelectric domains.The sample doped with 0.15 wt%of La_(2)O_(3) shows excellent electrical properties with TC=387℃,d33=332 pC/N,TKε=5.81×10^(−3)℃−1,Pr=20.66μC/cm^(2),Td=356℃.The significantly enhanced electrical properties and thermal depolarization temperature benefited from the donor substitution of La3+,decreasing the oxygen vacancy concentration in the lattice and possibly optimizing the ferroelectric domain structure of ceramics.

Colossal permittivity and ultralow dielectric loss in Nb-doped SrTiO_(3) ceramics

Defect engineering has been applied to prepare materials with modifiable dielectric properties.SrTiNbxO3(x=0,0.003,0.006,0.009,0.012)ceramics were synthesized using the traditional solid-state reaction method and sintered in a reducing atmosphere.All samples show excellent dielectric properties with giant permittivity(>3.5×10^(4))and low dielectric loss(<0.01).SrTiNb0.003O3 ceramic exhibits a colossal permittivity of 4.6×10^(4)and an ultralow dielectric loss of 0.005(1 kHz,room temperature)as well as great temperature stability in the range of(−60)–160℃.The mechanism of the presented colossal permittivity(CP)properties is investigated by conducting X-ray photoelectron spectroscopy(XPS)and analyzing activation energies.The results indicate that the introduction of Nb5+and the reducing sintering atmosphere together generated the formation of Ti^(3+)and V_(O)^(**).These defects further form Ti-V_(O)^(**)-Ti'_(Ti)defect dipoles,contributing to the coexisting giant permittivity and low dielectric loss in Nb-doped SrTiO_(3)(STN)ceramics.

Dielectric properties of BaMg_(1/3)Nb_(2/3)O_(3) doped Ba_(0.45)Sr_(0.55)TiO_(3) thin films for tunable microwave applications

Ba(Mg_(1/3)Nb_(2/3))O_(3)(BMN)doped and undoped B_(0.45)Sr_(0.55)TiO_(3)(BST)thin films were deposited via radio frequency magnetron sputtering on PUTiO_(2)/SiO_(2)/Al_(2)O_(3) substrates.The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy,resulting in an improved insulating properties of the BST film.Dielectric tunability,loss,and leakage current(LC)of the undoped and BMN doped BST thin flms were studied.The BMN dopant has remarkably reduced the dielectric loss(~38%)with no significant effect on the tunability of the BST film,leading to an increase in figure of merit(FOM).This is attributed to the opposing behavior of large Mg2+whose detrimental effect on tunability is partially compensated by small Nb5+as the two substitute Ti4+in the BST.The coupling between Mg″_(Ti)and V_(o)charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions.The LC of the films was investigated in the temperature range of 300-450K.A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from Mg″_(Ti),V_(o)and Nb_(Ti) charged defects.The carrier transport properties of the films were analyzed in light of Schottky thermionic emission(SE)and Poole-Frenkel(PF)enmission mechanisms.The result indicated that while the carrier transport mechanism in the undoped film is interface limited(SE),the conduction in the BMN doped film was dominated by bulk processes(PF).The change of the conduction mechanism from SE to PF as a result of BMN doping is atributed to the presence of uncoupled Nb_(Ti) stting as a positive trap center at the shallow donor level of the BST.