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1.
F. Weill J. L. Rehspringer P. Poix C. Kipelen J. C. Bernier 《Journal of Materials Science》1992,27(9):2316-2320
In order to understand the effect of niobium, tantalum, cobalt and magnesium cations on the ferroelectric properties of barium titanate we study solid solutions between BaTiO3 and BaM1/3N2/3O3 perovskite compounds where M=Co2+ or Mg2+ and N=Nb5+ or Ta5+. These solid solutions become cubic at room temperature for very weak additions. This result cannot be explained by geometrical consideration and suggests that an intermediate solid solution is made for weak additions. 相似文献
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Dielectric properties of lead zinc niobate (PZN) ceramics modified by barium zinc niobate (BZN) and BaTiO3 (BT) were investigated. By adding the modifier of BT and BZN, the stabilization of perovskite phase of PZN increased, but its Curie temperature decreased linearly with the amount of added modifier. Room temperature dielectric constant of PZN increased by addition of stabilizers up to 12 and 15 mol% of BZN and BT, respectively. The maximum room temperature dielectric constant was observed to be 7800 at 12 mol% of BZN, and 9800 at 15 mol% of BT, respectively. 相似文献
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Structural order in Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Nb2/3)O3 and Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics 总被引:4,自引:0,他引:4
The process and nature of structural ordering and the factors that influence them have been investigated in the microwave
dielectric perovskites, barium zinc tantalate (BZT), barium zinc niobate (BZN), and barium magnesium tantalate (BMT), sintered
at various temperatures. The samples were characterized mainly by X-ray powder diffraction and transmission electron microscopy.
The results show that short-range 1 : 1 B-site order features strongly in the early stages of ordering in BZT and BZN, but
it is extremely rare in BMT, for which most grains commence with 1 : 2 order. As sintering progresses, 1 : 1 order is replaced
by 1 : 2 long-range order in BZT and by disorder in BZN. Orientational variants of the ordered domains within grains occur
in similar numbers when order is fine-scale, but their distribution is less homogeneous in well-ordered samples. Local inhomogeneities
in the degree of order within grains, which will affect dielectric properties, correlate with both residual non-stoichiometry
and the presence of dislocations. Incompletely reacted starting materials which may persist to late stages of sintering can
also strongly influence order. Anomalously large ordered domains at grain boundaries are attributed to grain-boundary migration
accompanied by enhanced diffusion. The results indicate that with starting materials that are well-mixed and homogeneous at
the nanoscale, tailoring of physical properties should be possible by controlling the type and degree of order through chemical
composition.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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A. Beitollahi S. A. Mortazavi 《Journal of Materials Science: Materials in Electronics》2003,14(3):129-134
In this work attempt is made to study the effects of the level of the addition of two dopant systems, that is, Nb2O5/Co2O3 and Ba(Nb2/3Co1/3)O3 on the structure, microstructure, and dielectric properties of BaTiO3(BT) prepared by ceramic route. For the BT samples doped with 2 and 3 at % Nb2O5/Co2O3 a broad maxima for r–T variations was observed. Higher levels of addition, that is, 6, 8, and 10 at % Nb2O5/Co2O3, however, caused a drastic reduction in the magnitude of r and vanishing of maxima peaks observed. The reduction in the magnitudes of the r for these samples is related to the observed reduction of the tetragonality of doped BT samples as well as the existence of some non-ferroelectric extra phase, evidenced by our XRD analysis. The existence of this extra phase is also believed to be mainly responsible for the observed increase of the dielectric loss. For the BT samples doped with Ba(Nb2/3Co1/3)O3 perovskite solid solution, the r maxima peak could only be detected for the samples doped with 2 at %. In the case of the samples doped with 4, 6, 8, and 10 at % perovskite solid solution, however, a very uniform distribution of r–T was observed. The increase of the level of dopant for these series of samples was also seen to give rise in the reduction of the magnitude of r. However, this reduction was not as strong as the cases observed for the samples doped with 8 and 10 at % Nb2O5/Co2O3. XRD patterns obtained for these series of samples also revealed the reduction of tetragonality of the BT samples when doped with Ba(Nb2/3Co1/3)O3. Further, microstructural studies carried out by scanning electron microscopy (SEM) on both series of samples revealed a contrasting picture. While a uniform grain size distribution was observed for the whole series of the samples doped with Ba(Nb2/3Co1/3)O3, a non-uniform size distribution of grain sizes was observed in the case of samples doped with Nb2O5/Co2O3. This is thought to be due to the possible formation and non-uniform distribution of a liquid phase due to the formation of Ti-rich region in the shell region of Nb2O5/Co2O3-doped samples. The existence of such liquid phase, in case of Nb2O5/Co2O3-doped samples, would have the consequence of an increased rate of diffusion of Nb/Co into the BT cores leaving narrow compositional fluctuations for the shell regions. 相似文献
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Dielectric characteristics of Ba(Mg1/3Ta2/3)O3 ceramics (BMT ceramics) sintered at low temperatures with 2–3 wt% NaF additives were determined. A dielectric constant of 25 and extremely low dielectric loss (< 0.0001) were measured at 100 kHz and 1 MHz in BMT ceramics sintered under these conditions, and no frequency dependence of the dielectric constant was observed. This suggested that NaF as sintering additive had no harmful influence on the dielectric properties of the ceramics. 相似文献
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Dielectric properties of low-firing Pb(Mg1/3Nb2/3)1–x
Ti
x
O3-Bi2O3/Li2O ceramics are studied in this work. With the addition of Bi2O3/Li2O eutectic composition, the sintering temperature of PMN1–x
PT
x
could be lowered to 900° C. Relaxor behaviour of PMN1–x
PT
x
is enhanced by the incorporation of Bi2O3/Li2O due to the substitution of Bi+3/Li+ into the PMN1–x
PT
x
framework. Bi2O3/Li2O eutectic composition is used as a fluxing agent, Curie shifter and depressor. Evaporation of Bi2O3/Li2O and PbO during firing is checked and examined via energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) is used to clarify the Curie shifting and depressing effect of Bi2O3/Li2O. 相似文献
10.
The electrical properties of BaTi1?x M x O3 (M = Nb, Ta, Mo, W) ceramics (partial substitution of Group V (Nb, Ta) or VI (Mo, W) metals on the titanium site) have been studied by impedance spectroscopy. The results indicate that the Group VI metals (Mo and W) are less effective as donor dopants of barium titanate than are Nb and Ta because most of the Mo and W ions reside in the outer layer of the grains, raising its resistance. 相似文献
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This work continues our studies into the nature and mechanisms of phase transitions in K3Nb3B2O12 (KNB) crystals, which have a framework structure with spacious continuous channels and combine ferroelectric, ferroelastic, and superionic properties. Single crystals of KNB-based solid solutions in which Nb5+ is partially substituted with Ta5+ (KNBT) or Sb5+ (KNBS) are grown from off-stoichiometric melts. The KNBT solid solutions containing more than 15 at. % Ta are found to decompose at room temperature. The introduction of Ta leads to marked broadening of phase transitions but has little effect on the transition temperatures. KNBS solid solutions exist in a limited composition range. Increasing the Sb content shifts the high-temperature phase transitions to much lower temperatures and raises the electric conductivity of the crystals by 1–1.5 orders of magnitude. 相似文献
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P. Prabhakar Rao S. K. Ghosh Peter Koshy 《Journal of Materials Science: Materials in Electronics》2001,12(12):729-732
(M=Sm or Y) compounds were synthesized by the conventional powder compaction and high temperature solid state reaction technique. The calcined compounds were pelletized and sintered in the range 1275–1325 °C for 4 h. The dielectric and ferroelectric properties of the sintered pellets were measured and further characterised by X-ray diffraction and scanning electron microscopy (SEM). Sm and Y substituted compounds were found to have tetragonal structure and shown dielectric constants of 145 and 49 respectively at 1 MHz. The dielectric loss increases with frequency. Samarium compound had undergone a diffuse phase transition in the temperature range 195–210 °C whereas the same with Yttrium had shown the transition at around 25 °C. 相似文献
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Stabilization of the perovskite phase in PZN-BT-BZN ceramics prepared by solid-state sintering was investigated. With the
addition of BT and/or BZN, the amounts of perovskite phase in PZN ceramics increased, but the amount of pyrochlore phase decreased.
Optimum calcination conditions for this system, to obtain PZN ceramics with the minimum amount of the pyrochlore phase, are
a temperature range between 950 and 1000°C and a sintering time of 2–4 h. The perovskite phase of these systems could be 100%
stabilized by the addition of more than 7 mol% BT, 8 and 10 mol% BTZN and BZN, respectively.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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Kim ES Kang DH 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(5):1069-1074
Dielectric properties of (A(2+)(1/3)B(5+)(2/3))(0.5)Ti0(0.5)O(2) (A(2+) = Zn, Mg, B(5+) = Nb, Ta) ceramics were investigated at microwave frequencies. A single phase with tetragonal rutile structure was obtained through the entire compositions. Dielectric properties were strongly dependent on the structural characteristics. The specimens with B(5+) = Nb showed a larger dielectric constant than those with B(5+) = Ta due to the decrease of bond valence. Quality factors (Qf) of the specimens with B(5+) = Ta were larger than those with B(5+) = Nb. Temperature coefficient of the resonant frequencies (TCF) of (Zn(1/3)Nb(2/3) )0(0.5)Ti0(0.5)O(2) was larger than that of (Mg(1/3)Ta(2/3))0(0.5)Ti0(0.5)O(2). These results could be attributed to the changes of the temperature coefficient of dielectric constant and the degree of oxygen octahedral distortion. 相似文献
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Amodini Mishra S. N. Choudhary R. N. P. Choudhary V. R. K. Murthy Kamal Prasad 《Journal of Materials Science: Materials in Electronics》2012,23(1):185-192
A new lead-free perovskite Ba(Bi1/2Ta1/2)O3 was prepared by conventional ceramic fabrication technique at 1,200 °C/4 h in air atmosphere. The crystal symmetry, space
group and unit cell dimensions were determined from the experimental results using FullProf software. The crystallite size
and lattice strain were estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a
single-phase cubic structure with the space group Pm3m. EDAX and SEM studies were carried out in order to evaluate the quality and purity of the compound. Permittivity data showed
a low temperature coefficient of capacitance (T
CC
< 4%) up to +125 °C. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. Electric modulus
studies supported the hopping type of conduction in Ba(Bi1/2Ta1/2)O3. 相似文献
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《Materials Research Bulletin》2003,38(15):1957-1964
Powders of a Pb[(Zn1/3Ta2/3)0.2(Zn1/3Nb2/3)0.6Ti0.2]O3 system with gradual replacement of Zn by Mg were prepared by employing a B-site precursor method and developed structures were studied by X-ray diffractometry. Dielectric properties of the sintered ceramics were characterized under weak-field low-frequency conditions. A high maximum dielectric constant value of 38,000 (@1 kHz) was realized when 3/4 of octahedral Zn was replaced by Mg. Field-dependent polarization responses were also monitored at various temperatures to investigate ferroelectricity. Microstructures of the fractured ceramics were examined using a scanning electron microscope. 相似文献
20.
X. M. Chen Y. Suzuki N. Sato 《Journal of Materials Science: Materials in Electronics》1994,5(4):244-247
The sinterability of Ba(Mg1/3Ta2/3)O3 ceramics synthesized by solid-state-reaction methods was investigated. The poor sinterability of the present ceramics was found to be primarily due to the presence of satellite secondary phases of Ba5Ta4O15 and Ba4Ta2O9, and the nearly complete densification of Ba(Mg1/3Ta2/3)O3 ceramics was accomplished successfully by controlling the phase constitution of the calcined powders. For this purpose, enhanced ball-milling processes were found to be extremely effective. Moreover, excellent microwave dielectric characteristics (r = 24.5–24.7, Q = 26 000 at 9.8 GHz, and f = 1.7 p.p.m. C–1) were attained in the dense Ba(Mg1/3Ta2/3)O3 ceramics without additives. 相似文献