Effect Of Niobium Doping Research Articles

Effects of Niobium-Doping on the Structure and Electrical Properties of (Ba,Bi,Na)TiO<SUB>3</SUB>-based P<I>T</I><SUB>c</SUB>R Ceramics

采用固相反应法制备了施主掺杂浓度不同的Nb2O5（分别为0.1mol%、0.3mol%、0.5mol%、0.7mol%）掺杂（Ba,Bi,Na）TiO3基PTCR陶瓷.对其微观结构及电性能进行研究发现：随着Nb2O5掺杂浓度的增加,陶瓷晶粒尺寸先变大后变小,室温电阻率也随之先减小后增大,说明Nb2O5的掺杂量存在一个临界施主掺杂浓度.当Nb2O5施主掺杂量为临界施主掺杂浓度0.5mol%时,获得了居里温度Tc为183℃、室温电阻率ρ为1.06×10^3Ω.cm、升阻比ρmax/ρmin为1.0×10^4的高温无铅PTCR陶瓷.通过交流复阻抗谱分析,探讨了Nb2O5施主掺杂在该PTCR陶瓷中的作用机理.

Effects of niobium doping on lead zirconate titanate films deposited by a sol–gel route

Niobium (Nb)-doped lead zirconate titanate (PZT) films have been prepared on platinized silicon substrates using a sol–gel method. The Zr/Ti ratios of the films are 53/47 and 40/60, and the Nb doping level ranges from 0 mol% to 3 mol%. Similar to the cases in bulk ceramics, after the doping with Nb, the remanent polarization Pr, effective transverse piezoelectric coefficients e31,c and pyroelectric coefficient p of the PZT films increase; but the longitudinal effective piezoelectric coefficient d33,c remains roughly unchanged. At the optimum Nb doping levels, the observed Pr, −e31,c and p reach a maximum value of 30 μC/cm2, 18 C/m2 and 350 μC/m2 K, respectively, for the PZT (53/47) films, and 37 μC/cm2, 7.9 c/m2 and 370 μC/m2 K for the PZT (40/60) films. Our results also reveal that there exist linear relations between p, e31,c/er and Pr.

Effect of niobium doping on the densification and grain growth in alumina

The effect of niobium doping on the densification and grain growth of nano-sized α-Al 2O 3 powders during sintering has been investigated. The dopant concentration added ranged from 0.1 to 0.5 mol%. It was observed that addition of niobium oxide could improve the densification of the pure alumina with a lower sintering temperature, a shorter sintering time. The effect is strengthened by increasing the amount of dopant. It also demonstrated that niobium dopant significantly promotes the grain growth of alumina during sintering and the grain size of alumina increases with increasing the amount of dopant in the added range.

STRUCTURAL AND ELECTRICAL PROPERTIES OF Nb5+ SUBSTITUTED PZT CERAMICS

The effect of niobium doping on the structure and electrical properties with the following compositions Pb ( Zr 0.52 Ti 0.48)1-5X/4 Nb X O 3 with 0<x<0.025 was investigated. The materials were prepared by the usual ceramic technique using high purity raw materials. Disc-shaped samples of each compositions were sintered at 1250°C for 3 hours. The sample structure was determined by X-ray diffractometry. The average grain size, the maximum dielectric permittivity and the remnant polarization first increases up to x = 0.005 concentration of Nb 5+ and then decreases with higher concentration of niobium, while the coercive field does not show any variation. The transition temperature decreases with the increase in niobium concentration.

Effect of niobium doping on the properties and ferroelectric domain structures of Bi4Ti3O12 ceramics

Here we report the influence of niobate doping on the electrical properties and domain structures of bismuth layer-structured ceramics Bi4Ti2.98Nb0.02O12 (BTNb0.02) and Bi4Ti2.92Nb0.08O12 (BTNb0.08). The result reveals that Nb doping can improve the properties of ceramics and change the domain structures of ceramics. Domain walls in BTNb0.02 were mainly 90° and in BTNb0.08 were mainly parallel to the a–b plane. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of niobium doping on the piezoelectric properties of sol–gel-derived lead–zirconate–titanate films

Sol–gel-derived lead–zirconate–titanate (PZT) films doped with various amounts of niobium (Nb) have been spin coated on silicone substrates, and their remanent polarization Pr, and effective longitudinal and transverse piezoelectric coefficients (d33,c and e31,c) as well as the pyroelectric coefficient p, have been measured. The Zr/Ti ratio of the films is 53/47. Our results reveal that the Nb-dopant effects on the PZT films are very similar to the experimentally known effects on the corresponding bulk ceramics, i.e., enhancing both the longitudinal and transverse piezoelectric properties. However, because of the substrate clamping effect, the exact enhancement in the longitudinal piezoelectric properties cannot be evaluated by the d33,c measurement on the film samples. Accordingly, the observed d33,c value of the Nb-doped PZT films remains almost unchanged while the observed −e31,c (as well as Pr and p) increases with increasing Nb concentration, showing an optimum Nb concentration of 2 mol %. For the PZT film doped with 2% Nb, the observed values of Pr, d33,c, −e31,c, and p are about 30 μC/cm2, 95 pm/V, 18 C/m2, and 350 μC/m2 K, respectively.

Effects of interface properties on densification in a grain compact during sintering

A theoretical approach to describe the relationship between the interface properties and densification for sintering materials is presented. This approach is developed by assuming simplified grain boundary geometry, where scaling is imposed. In general, the results are in good agreement with theoretical calculations from other studies, as well as with available experimental data. The model predicts a higher densification rate in particle agglomerates, if grain growth is inhibited. Hence, qualitative predictions lead to a plausible explanation, for instance, for the effect of niobium doping on PZT ceramics experimentally reported in the literature. The bulk and shear viscosities, as well as the sintering stress are reported.

Effects of niobium doping on microstructures and ferroelectric properties of bismuth titanate ferroelectric thin films

Bi 4Ti 3O 12 thin films doped with 3 mol.% niobium were prepared on Pt/Ti/SiO 2/Si substrates by sol–gel method. The niobium-doped Bi 4Ti 3O 12 (Nb–BiTiO) films annealed at 700 °C for 30 min in oxygen showed randomly oriented layered perovskite structures and was composed of plate-like and rod-like grains with no crack. The remanent polarization (2 P r) and coercive field (2 E c) of the Nb–BiTiO film annealed at 700 °C were 28 μC/cm 2 and 110 kV/cm, respectively. In addition, the film showed good switching endurance under bipolar pulse at least up to 4.5×10 10 cycles. Substitution of Nb in BiTiO thin films was effective for reducing the oxygen vacancies and generating good ferroelectric properties.

Influence of the niobium dopant concentration on the Pb(Zr0.54Ti0.46)O3 ceramics sintering and final properties

The effect of niobium doping on the structure and properties of piezoelectric PZT ceramics is studied. Samples of the system Pb(Zr0.54Ti0.46)O3 + x wt % Nb2O5, (x = 0.2, 0.4, 0.6, 0.8, 1.0) were obtained by calcination of mixed oxides and subsequent sintering. Structural analysis (XRD and Optical Microscopy) was carried out. All compositions lead to single-phase tetragonal samples. As a general tendency, grain size and porosity decrease as the niobium concentration increases. Important fibber texture appeared in all samples, with crystallite [001] direction parallel to sample symmetry axes. Texture becomes more intense as the Nb concentration increases. Studying the polarization and the piezoelectric constant d33, we observe a maximum of these properties for the intermediate value x = 0.8.

Effect of niobium doping on the microstructure and electrical properties of strontium titanate thin films for semiconductor memory application

Niobium doped strontium titanate [Sr(Ti1−xNbx)O3] thin films (≅40 nm) were deposited on Ir substrates using rf magnetron sputtering. The effect of Nb content (x=0, 0.001, 0.01, and 0.05) on the microstructure, dielectric constant, dielectric dispersion, and leakage current was studied. It was found that with increasing Nb content the dielectric constant decreased, probably owing to an observed decrease in grain size. The dielectric dispersion of all the Nb-doped ST films was lower than that of undoped ST film deposited at the same temperature and pressure. For the case of x=0.01, dispersion as low as 0.425% per decade was observed. The leakage current was found to increase slightly for x=0.001 and x=0.01, and drastically for the x=0.05 case.

Use of Ferroelectric Hysteresis Parameters for Evaluation of Niobium Effects in Lead Zirconate Titanate Thin Films

The effects of niobium doping on the hysteresis parameters of sol—gel Pb1.1−(x/2)(Zr0.53Ti0.47)1−xNbxO3 (0, x, 0.05) have been reported for two sets of films with analogous grain size and degree of (111) texture but with different surface microstructures. For both sets, a strong continuous decay of the remnant and maximum polarizations and slope of the hysteresis loop at the coercive field was observed with increasing niobium concentration. The field dependence of the remnant polarization for any given niobium‐doped film was identical to the functional field dependence of the undoped reference film, if multiplied by a niobium‐concentration‐dependent constant. Although the maximum and remnant polarizations decayed as the dopant level increased, their difference remained the same value as that of the undoped film at any given field. The width of the loop (at zero polarization) was insensitive to the niobium concentration at any given field. A linear increase in coercive field asymmetry (up to 40 kV/cm) was observed with niobium addition, yet was field independent and, thus, electrostatic in origin. Niobium governed switching through a reduction of the number of switching domains, without changing the total lattice polarization response. Microstructure‐related effects on switching, such as decreased volume fraction of ferroelectric material or field‐screening effects due to the presence of a pyrochlore second phase, were eliminated as the origin of the hysteresis changes. This paper has demonstrated how hysteresis features and their field dependencies can be used to separate the effects of niobium‐induced microstructural changes from niobium lattice doping influences on the hysteresis loops.

Role of Niobium in Magnesium Titanate Microwave Dielectric Ceramics

The effect of niobium doping on MgTiO3 ceramics was evaluated in terms of microstructure and microwave dielectric properties. Pure and doped MgTiO3 dense ceramics were produced. Doping levels of niobium were 0.5,1, and 2 at.% of Nb5+. Phase assemblages were examined by XRD and checked by EDS during microstructural observations by SEM. Microwave dielectric properties were measured at 8 GHz. Dielectric permittivity was not much affected by doping. Q decreased for the sample with the higher Nb content because of the presence of a second phase. For low Nb contents, a solid solution was formed and Q even increased. An explanation is presented based on the elimination of lattice defects.

Effect of niobium doping on the atmospheric oxidation of Fe-Si-Al magnetic alloys

Magnetic alloys having a composition around Fe-10Si-5Al are called “Sendust”. Doping with high valence metal elements, such as titanium, vanadium, zirconium and niobium, is considered to be effective in improving the corrosion resistance of Sendust, but systematic data have not been reported. In the present work, the effect of niobium doping on the atmospheric oxidation of Sendust was studied with XPS and ellipsometry. In air with a relative humidity (RH) of 42.8–90% at 80°C, oxide films grew rapidly on both doped and undoped Sendust in the initial 2 days. After 20 days, the thickness reached 5–6 nm with mirror finished specimens (by ellipsometry), thinner than on pure iron ( ca 7 nm). The films were thicker on specimens polished with No. 600 emery paper (by XPS). The films were estimated to be a mixture of silica-alumina composite oxides and Fe(III)-oxyhydroxides. With RH= 42.8% (no condensed water on the surface), the proportions of Si(IV) and Al(III) in the film were larger with the niobium doped Sendust than with the undoped Sendust. This suggests that a small amount of niobium doping may improve the corrosion resistance of Sendust in a dry atmosphere. With RH= 90% (with condensed water on the surface) the film composition did not show a significant difference with doping, in agreement with the results of anodic polarization experiments, indicating that under wet conditions no doping effect may be expected.

Effect of niobium doping on the properties of molybdenum sulfides as cathode materials

Poorly crystalline molybdenum sulfides are promising candidates as cathode materials which require good electronic and ionic conductivity. Poorly crystalline molybdenum sulfide films with a large range of sulfur contents were successfully synthesized by the activated reactive evaporation technique. Raman spectra of the poorly crystalline films showed dual structure characteristics corresponding to 2H-MoS2 and amorphous MoS3. The films with the above structure demonstrated significantly improved intercalation ratios of lithium atoms, thereby enhancing the energy density of the secondary lithium batteries. However, the current density was lower because of the high electronic resistivity of the films. Niobium, acting as an acceptor, was, therefore, doped into the molybdenum sulfide films to decrease the electronic resistivity. Decrease in the resistivity by about three orders of magnitude was observed.