Song Tianxiu

Effect of Grain Size of BaTiO3 Ceramics on Dielectric Properties

BaTiO3 ceramics with different grain size from 0.56 to 120 μm were prepared by the conventional solid state processing and two-stage sintering method using ultrafine BaTiO3 powders prepared by a sol-gel method. Dielectric, ferroelectric and piezoelectric properties of BaTiO3 ceramics with different grain size were investigated. The grain size effect of BaTiO3 ceramics on dielectric appeared clearly. The coercive field showed a maximum value of 7.14 kV/cm at the grain size of 1.1 μm and piezoelectric constant d33 showed a maximum value of 204 pC/N at 8.9 μm. The remanent polarization of BaTiO3 ceramics increased with the increasing of the grain size.

Diffuse Phase Transition of Ba0.92Ca0.08(Ti0.82Zr0.18)O3 Based Ceramics

Ba0.9175Ca0.08Nd0.0025(Zr0.18Ti0.8175-xYxMn0.0025)O3(x = 0, 0.5%, 0.75%, 1.0%, 1.5% and 2.0% mol) ceramics are synthesized by the conventional solid state processing. X-ray diffraction patterns show that all the compositions have an only tetragonal BaTiO3 structure at room temperature. The dielectric constant of samples decrease, dielectric peak temperature (Tm ) shifts toward lower temperature and the frequency dispersion becomes strong and the more pronounced DPT (Diffuse Phase Transitions) behavior as the content of Y increases. The degree of deviation from the Curie–Weiss law is found to increase and the value of the parameter γ is from 1.82 to 1.96 with the increasing amount of Y3+.

The Dielectric Behavior of BaTiO3 Based Ceramics Doped With La/Mn

BaTiO3 based ferroelectric ceramics (with some additives such as SnO2 and ZrO2 etc) were prepared by solid state reaction. Mn2+ or Mn3+ as an acceptor substituting for Ti4+ in B sites and La3+ as a donor substituting for Ba2+ in A sites were co-doped in BaTiO3 based ceramics. The effect of the donor and acceptor (La/Mn) on the dielectric dispersion properties of BaTiO3 based ceramics was investigated. The Mn = 1.6% mol and La = 0, 0.10%, 1.1%, 1.4% mole. When the content of La (donor) increased, the ferroelectric relaxor behavior was observed and the dielectric permittivity decreased. When La varied from 0% to 1.4% mol (Mn = 1.6% mol), remnant polarization from 7.96 to 0.58 μC/cm2, coercive field from 4.4 to 1.0 kV/cm, and piezoelectric constant d33 from 90 to 35 pC/N respectively.

Dielectric Properties of Ba(Ti0.91Zr0.09)O3 Ceramics Doped with CuO

The structure and dielectric properties of Ba(Ti 0.91 Zr 0.09 )O 3 ceramics with CuO doped were investigated. XRD indicates that compositions have single tetragonal phase for x (CuO) ≤ 0.38wt% at room temperature and shows the increase in the distance of (110) lattice plane. A decrease in grain size is observed when the content of CuO increase. For x = 0, only one dielectric constant peak in ϵ -T curve is observed at TC. It appears a normal ferroelectric behavior. With increasing CuO, another dielectric constant peaks in ϵ -T curve is observed at the transition point (T 1 ) from tetragonal to orthorhombic. At Orthorhombic-Tetragonal phase transition point, larger diffuseness of the phase transition (▵Tdif), the frequency dispersion (▵Trelax) and γ are observed and a diffuse phase transition at Tetragonal-Cubic phase transition point. The physical mechanism of the relaxation process is discussed.

The Dielectric Dispersion Properties of BaTiO3 Based Ferroelectric Ceramics Doped with Nb/Mn

BaTiO3 based ferroelectric ceramics (with some additives such as ZrO2, SnO2 and ZrO2 etc) were prepared by solid state reaction. Mn2+ or Mn3+ as an acceptor and Nb5+ as a donor substituting for Ti4+ in B site were co-doped in BaTiO3 based ceramics. The effect of the mole ratio of donor and acceptor (Nb/Mn) on the dielectric dispersion properties of BaTiO3 based ceramics co-doped with Nb/Mn was investigated. The Mn = 1.6% mol and Nb = 0, 0.18%, 1.0%, 1.1%, 2.0% mole. The ratio of donor and acceptor increase, dielectric dispersion behavior was observed and the dielectric constant decrease. When Nb varied from 0% to 2.0% mol (Mn = 1.6% mol), remnant polarization from 8.91 to 0.59 μC/cm2, coercive field from 4.5 to 1.1 kV/cm, and piezoelectric constant d33 from 90 to 13 pC/N respectively. The dielectric relaxation behavior of BaTiO3 based ceramics co-doped with Nb/Mn was discussed.

Structure and Dielectric Properties of Ba(Ti0.9Zr0.1)O3 Ceramics Doped with Bi

Ba1-xBix(Ti0.9Zr0.1)O3 (x = 0.01, 0.02, 0.03, 0.04 mol) ceramics were prepared by solid state reaction. XRD analysis indicates that the samples are tetragonal crystal structure and when x > 0.03 mol the second phase appeared. The grain size of ceramics decreased with the increase of x. The temperature dependence of dielectric constants at different frequencies show that the behavior of diffused phase transition existed, and x≥0.02 mol exhibited typical relaxor ferroelectric characteristic. The relaxor characteristics were discussed using Lorenz formula.

Effects of Defects on Relaxation Behavior of Nd-Doped BCZT Ceramics

(Ba0.92−xCa0.08Ndx)(Ti0.82Zr0.18)O3 (0 ≤ x ≤ 0.02) were prepared through solid reaction route. The relaxor behavior of (Ba0.92-xCa0.08Ndx)(Ti0.82Zr0.18)O3 have been studied. When x = 0, a broad dielectric peak with frequency dispersion occurred, with increasing Nd3+ content, the relaxation and diffuseness degree was strengthened. Atomic computer simulation has been used to predict the energy for different defect associates [Nd•Ba + NdTi′] and [4Nd•Ba + VTi′′′′]. Local random field induced by such off-center Nd3+ ions and [Nd•Ba + NdTi′] and [4Nd•Ba + VTi′′′′] gives rise to the relaxor behavior.

The Effect of MgO on the Structure and Dielectric Properties of α-BZN Ceramics

The effect of MgO doping (in which Bi3+ or Zn2+ substituted by Mg2+) on the structure and dielectric properties of α-BZN ceramics are investigated. X-ray diffraction patterns show that (Bi1.5Zn0.5)(Zn0.5−xMgxNb1.5)O7 ceramics have an only cubic pyrochlore structure (α-BZN), while the secondary phase is found even with the addition of 0.05 mol Mg2+ for (Bi1.5−xMgxZn0.5)(Zn0.5Nb1.5)O7 ceramics. With the increasing of Mg content, the grain size of (Bi1.5−xMgxZn0.5)(Zn0.5Nb1.5)O7 increases while the (Bi1.5Zn0.5)(Zn0.5−xMgxNb1.5)O7 has no obvious change. All the compositions exhibit a typical relaxation behavior with strong frequency dispersion in the low-temperature range. The degree of frequency dispersion can be measured by △Tm = Tm (1MHz)-Tm (100 kHz).

Study of structure and dielectric properties of Bi1.5Zn1+xNb1.5O7+x ceramics

ABSTRACT Bi1.5Zn1+xNb1.5O7+x (x = 0.005, 0.01, 0.015, 0.02) ceramics were prepared and the structure, crystal chemistry and dielectric properties were investigated. The results revealed that the samples showed a cubic pyrochlore structure when x ≤ 0.015 mol and the second phase occurred at x = 0.02 mol. With the increase of x, the lattice constant and the average distance R(A-O′) increased and the bond valance theory showed that the AV(O′)[A4] and oxygen ξ parameter of 48f(O) gradually decreased. The dielectric constant decreased and the dielectric loss increased. The activation energy increased from 0.2925eV to 0.3043eV by using the Arrhenius equation.

Dielectric Properties of Ca Doping α-BZN Ceramics

Bi1.5-δCaδZnNb1.5O6O′ (0≤δ≤0.3) ceramics samples were prepared by conventional solid-state reaction methods. The effect of Ca2+ doping on dielectric properties, crystal chemistry characteristics and relaxor behavior of α-BZN pyrochlore were investigated. The dielectric constant decreases with increasing Ca content. The bond valance calculations revealed the dielectric constant was proportional to bond valance sum of O′ anions. When δ = 0, the dielectric relaxation is attributed to hopping of A-site cations, however, when δ > 0, the declining relaxor behavior is closely related to the increasing A-O′ bond valance, the change from perfect octahedral to regular cube.