Liqin Zhou

Dependence of the Structural and Dielectric Properties of Ba1-xSrxTiO3 Ceramic Solid Solutions on Raw Material Processing

Abstract The structures and dielectric properties of Ba1-xSrxTiO3 ceramic solid solutions in the whole x range and their dependence on the material processing are investigated. A short time pre-calcination milling–mixing of the precursor powders causes compositional inhomogeneity and thus a diffuse phase transition. For long milling–mixing time, the diffuse phase transition is observed only in the SrTiO3 rich compositions (x>0·8).

Dielectric properties of bismuth doped Ba1-xSrxTiO3 ceramics

Abstract The dielectric properties of bismuth (5 at.%) doped Ba 1− x Sr x TiO 3 ( x =0, 0.2, 0.4, 0.6 and 0.8) ceramics are investigated. Bi doping significantly decreases the dielectric permittivity maximum of ferroelectric–paraelectric phase transition of Ba 1− x Sr x TiO 3 solid solutions and shifts the ferroelectric–paraelectric phase transition temperature to lower temperatures for the x =0, 0.2, 0.4 and 0.6 compositions but to higher temperature for the x =0.8 composition. Bi doped BaTiO 3 still exhibits normal ferroelectric characteristic while a relaxor behavior was observed in Bi doped Ba 1− x Sr x TiO 3 and the degree of the diffuseness and the relaxation increases as x increases. A random electric field is suggested to be responsible for the relaxor behavior observations.

The effects of La on the dielectric properties of lead iron tungstate Pb(Fe2/3W1/3)O3 relaxor ceramics

Abstract La doped samples were used to study the effects of this dopant on the structural and dielectric properties of Pb(Fe 2/3 W 1/3 )O 3 (PFW) relaxor ceramics. La doping leads to a decrease in the lattice constant of the cubic PFW perovskite and to the precipitation of increasing amounts of a second phase, PbWO 4 . A decrease of dielectric permittivity maximum, e rmax , a shift of transition temperature, T 0 , to lower temperatures, and an increase of diffuseness, δ , are also observed. Undoped and La doped PFW show a p-type conduction. The resistivity vs La content shows a “V-like” curve. The aging behavior of the samples are also altered by the presence of the dopant. The aging decreases with increasing the La content up to 5 at% and increases after that. Charge compensation and defect associations in the La doped samples are discussed and suggested to explain the electrical properties and the aging behavior.

Synthesis and characterization of lead iron tungstate ceramics obtained by two preparation methods

Abstract Lead iron tungstate ( Pb(Fe 2 3 W 1 3 ) O 3 ) is difficult to sinter as a single phase perovskite ceramic. Side reactions lead to undesirable second phases damaging the dielectric properties of the sintered material. Understanding these reaction routes is necessary to eliminate them and to improve on the properties of these ceramics. Lead iron tungstate ceramics were sintered from powders prepared by reaction of mixtures of the three oxides, or by reaction of prereacted iron oxide and tungsten oxide with lead oxide, in an attempt to control the formation of the perovskite phase. The reaction sequences, different in both cases, lead to a higher yield of the perovskite phase when the prereacted powders were used, avoiding therefore the presence of undesirable phases. The microstructures and dielectric properties of the sintered ceramics obtained by both methodologies are reported and compared. The prereacted intermediate phase method leads to a more ordered perovskite structure with better dielectric characteristics.

The characteristics of the diffuse phase transition in Mn doped Pb(Fe2/3W1/3)O3 relaxor ceramics

The characteristics of the diffuse phase transition of Pb(Fe2/3W1/3)O3 relaxor ceramics doped with different amounts of Mn are investigated. The freezing temperature Tf, obtained by fitting the ω,Tmax to the Vogel–Fulcher relationship, clearly changes with the Mn content. It increases as the Mn content increases, approaching the Tmax(1 MHz) value of the relaxor curve. A concomitant decrease in the frequency dispersion of Tmax is also observed. The freezing temperature also increases as the 1:1 order of Fe3+ and W6+on B sites increases by air annealing but decreases by oxygen annealing. It is suggested that the Mn ions, which are predominantly compensated by oxygen vacancies, form with them defect pairs and that these pairs can couple to the spontaneous polarization vectors, increasing the correlation between the dipole moments and originating the increase of the freezing temperature. It is further suggested that filling up the oxygen vacancies by oxygen annealing will decrease the defect pairs and cause t...

Effects of annealing treatment on the dielectric properties of manganese-modified Pb(Fe2/3W1/3)O3 ceramics

The dielectric properties of thermally treated manganese doped Pb(Fe2/3W1/3)O3 (PFW) ceramics were investigated. Modifications of the dielectric properties by thermal annealing were observed. Air annealing causes a sharpening of the dielectric permittivity and an increase of the permittivity maximum values, more pronounced as the amount of manganese dopant increases. Oxygen annealing does not cause evident variations in the dielectric permittivity curve. The presence of oxygen vacancies is evinced by thermal gravimetric measurements. The role of oxygen vacancies, as well as the associations of manganese ions with oxygen vacancies, on the annealing process, is proposed and discussed.

Ordering in lead iron tungstate relaxor ceramics

Abstract The ordering behavior of sodium doped lead iron tungstate ceramics, Pb 1 − x Na x [ Fe (2 − x) 3 W (1 + x) 3 ]O 3 , was investigated together with their dielectric properties. The 1:1 type ordering of iron and tungsten cations, on the B sites, was evidenced by h + 1 2 , k + 1 2 , 1 + 1 2 superlattice reflections in both X-ray and transmission electron microscopy diffraction. The ordering degree increases with Na content when Na ≤ 8 at% and decreases when Na > 8 at%. Besides the perovskite PFW phase, a second phase, PbWO 4 , was observed in Na doped PFW ceramics and its amount increases with increasing Na content. The dielectric permittivity decreases with the increase in the Na content, while the diffuseness increases. It is suggested that the substitution of Na + for Pb 2+ leads to a decrease in the charge imbalance between ordered and disordered ] regions, enhancing the ordering of PFW ceramics. The competition between the enhancement of ordering and the formation of the PbWO 4 phase is suggested to be responsible for the decrease of ordering, when Na > 8 at%.

Dielectric properties and aging effects of manganese modified lead iron tungstate relaxor ceramics

Mn-doped samples were used to study the effects of Mn dopant on the dielectric properties of PFW ceramics, especially on its aging behavior, since they could add some knowledge on the role of lattice defects on the aging mechanisms of this relaxor ferroelectric. Mn doping does not cause marked changes in the maximum of permittivity ({var_epsilon}{sub rmax}), transition temperature (T{sub 0}), and diffuseness coefficient ({delta}) under the solubility limit, whereas the resistivity increases significantly with increasing the Mn content. Mn-modified PFW ceramics exhibit evident aging behavior and its level increases with the increase in Mn content. The aging shows strong dependence on the frequency and has a log-linear function of aging time. Probable lattice defects in the ceramics are discussed and it is suggested that the acceptor Mn ions are dominantly compensated by oxygen vacancies, providing reorientable dipole pairs which are responsible for the aging process of Mn-modified PFW ceramics.

Relaxor Behavior of (Sr0.8Ba0.2)TiO3 Ceramic Solid Solution Doped with Bismuth

The dielectric properties of (Sr0.8Ba0.2)1-1.5xBixTiO3 ceramics in the range 0 ≤ x ≤ 0.18 are investigated. A ferroelectric relaxor behavior is observed. The degree of the diffuseness and the relaxation of the phase transition increases as the Bi content increases. A random electric field is suggested to be responsible for the relaxor behavior observations. The dependence of the diffuseness on the grain size is presented.

DIELECTRIC PROPERTIES OF COBALT AND CHROMIUM DOPED LEAD IRON TUNGSTATE RELAXOR CERAMICS

Abstract The effect of Co and Cr doping on the dielectric properties of Pb(Fe2/3 W1/3)O3 relaxor ceramics is analysed in this work. No second phases were detected for Co doped PFW for Co < 7.5 at%. On the other hand, a Pb2WO5 second phase was identified in Cr doped PFW. Both Co and Cr decrease the permittivity maximum and shift transition temperature to high temperatures. Relaxor aging behaviour was observed for both doped compositions, being more pronounced for Cr doped PFW. Oxygen annealing post-sintering treatment increases ermax and the sharpening of temperature dielectric response of Cr doped PFW. The observed dielectric modifications are discussed in relation to the probable defects present in the ceramics