ZnO Nb Research Articles

Effect of Ca substitution on phase compositions and dielectric properties of Bi2O3–ZnO–Nb2O5 pyrochlore ceramics

Abstract The phase evolution, microstructure and dielectric properties in the Ca 2+ substituted Bi 2 O 3 –ZnO–Nb 2 O 5 system were studied. The crystalline phases of the [Bi 1.8 (Ca x Zn 1− x ) 0.2 ](Zn 0.6 Nb 1.4 )O 7 pyrochlores (0.0≤ x ≤1.0) depend greatly on the ratio of ionic radius A/B. With the Ca 2+ substitution for Zn 2+ in the A site, the crystalline phase transformed from cubic to monoclinic and pure monoclinic phase was obtained for x ≥0.5. As the x value increased from 0.5 to 1.0, the permittivity in the microwave range decreased from 76.4 to 75.0, the quality factor Qf value increased from 1800 to 4700 GHz, and the TCF value shifted from −99 to −147 ppm/°C.

Resistance-switching behaviour in ZnO–Nb 2 O 5 thin films for non-volatile memory application

The microstructure and resistance switching characteristics of polycrystalline ZnO-Nb 2 O 5 thin films prepared by the sol-gel method on indium tin oxide (ITO)/glass substrates at different annealing temperatures followed by annealing in oxygen have been investigated. The selected-area diffraction pattern showed that the deposited films exhibited a polycrystalline microstructure. The Pt/ZnO-Nb 2 O 5 /ITO/glass device exhibits reversible and steady bistable resistance switching behaviour with a narrow dispersion of resistance states and switching voltages. The resistance ratios of high-resistance state to low-resistance state were in the range of 1-2 orders of magnitude within 200 test cycles.

Mg-substituted ZnNb 2O 6–TiO 2 composite ceramics for RF/microwaves ceramic capacitors

Microstructure and microwave dielectric properties of Mg-substituted ZnNb 2O 6–TiO 2 microwave ceramics were investigated. Mg acted as a grain refining reagent and columbite phase stabilization reagent. With an increasing Mg content, the amount of ixiolite (Zn, Mg) TiNb 2O 8 decreased, and the amount of (Zn 0.9Mg 0.1) 0.17Nb 0.33Ti 0.5O 2 and columbite increased. ZnO–Nb 2O 5–1.75TiO 2–5 mol.%MgO exhibited excellent dielectric properties (at 950 °C): ɛ r = 35.6, Q × f = 16,000 GHz (at 5.6 GHz) and τ f = −10 ppm/°C. The material was applied successfully to make RF/microwaves ceramic capacitor, whose self-resonance frequency was 19 GHz at low capacitance of 0.13 pF.

Microwave dielectric properties and structure of ZnO–Nb 2O 5–TiO 2 ceramics

Ceramic samples based on ZnO–Nb 2O 5–TiO 2 compositions have been prepared using solid state ceramic route. The work was carried out over a wide range of initial ZnNb 2O 6 and Zn 0.17Nb 0.33Ti 0.5O 2 compounds concentration. The crystal structure and microstructure developments were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was shown that the phase compositions of the samples present itself a columbite type and mixture of two phases—solid solutions of columbite and rutile types.The sintering behavior, permittivity, its temperature coefficients and quality factor had been characterized for ceramic samples in depending on compositions. The permittivity of the samples in this system is within the limits from 24 to 80, τ ɛ from 150 to −560 ppm/°C. For the samples with τ ɛ ∼ 0, ɛ r ∼ 43.8 and Q· f = 35000 GHz at f = 9 GHz. The comparatively low sintering temperature (≤1080 °C) and high dielectric properties in microwave range make these ceramics promising for application in electronics.

A low-firing microwave dielectric material in Li 2O–ZnO–Nb 2O 5 system

LiZnNbO 4 ceramic was fabricated by the conventional solid state reaction method and its microwave dielectric properties were reported for the first time. The phase structure, microstructure, and sintering behavior were also investigated. The LiZnNbO 4 ceramic could be well densified at around 950 °C and demonstrated high performance microwave dielectric properties with a low relative permittivity ~ 14.6, a high quality factor (resonant frequency/dielectric loss) ~ 47, 200 GHz (at 8.7 GHz), and a negative temperature coefficient of resonant frequency approzmiately −64.5 ppm/°C. The LiZnNbO 4 ceramic is chemically compatible with Ag electrode material at its sintering temperature. It can be a promising microwave dielectric material for low-temperature co-fired ceramic technology.

LiZnNb 4O 11.5: A novel oxygen deficient compound in the Nb-rich part of the Li 2O–ZnO–Nb 2O 5 system

A novel lithium zinc niobium oxide LiZnNb 4O 11.5 (LZNO) has been found in the Nb-rich part of Li 2O–ZnO–Nb 2O 5 system. LZNO, with an original α-PbO 2 related structure, has been synthesized by the routine ceramic technique and characterized by X-ray diffraction and transmission electron microscopy (TEM). Reflections belonging to the LZNO phase, observed in X-ray powder diffraction (XRPD) and electron diffraction, have been indexed as monoclinic with unit cell parameters a=17.8358(9) Å, b=15.2924(7) Å, c=5.0363(3) Å and γ=96.607(5)° or as α-PbO 2-like with lattice constants a=4.72420(3) Å, b=5.72780(3) Å, c=5.03320(3) Å, γ=90.048(16)° and modulation vector q=0.3 a *+1.1 b * indicating a commensurately modulated α-PbO 2 related structure. The monoclinic cell is a supercell related to the latter. Using synchrotron powder diffraction data, the structure has been solved and refined as a commensurate modulation (superspace group P112 1 /n( αβ0)00) as well as a supercell (space group P2 1 /b). The superspace description allows us to consider the LZNO structure as a member of the proposed α-PbO 2- Z (3+1)D structure type, which unifies both incommensurately and commensurately modulated structures. HRTEM reveals several types of defects in LZNO and structural models for these defects are proposed. Two new phases in Li 2O–ZnO–Nb 2O 5 system are predicted on the basis of this detailed HRTEM analysis.

Effect of oxygen pressure on structure and properties of Bi 1.5Zn 1.0Nb 1.5O 7 pyrochlore thin films prepared by pulsed laser deposition

The Bi 2O 3–ZnO–Nb 2O 5 (BZN) cubic pyrochlore thin films were prepared on Pt/TiO 2/SiO 2/Si(1 0 0) substrates by using pulsed laser deposition process. The oxygen pressure was varied in the range of 5–50 Pa to investigate its effect on the structure and dielectric properties of BZN thin films. It is found that oxygen pressure during deposition plays an important role on structure and other properties of BZN films. The BZN films deposited at temperature of 650 °C and at O 2 pressure of 5 Pa have an amorphous BZN and Nb 2O 5 phases but exhibits a cubic pyrochlore structure with a preferential (2 2 2) orientation when the oxygen pressure increases to 10 Pa. Dielectric constant and loss tangent of the films deposited at 10 Pa are 185 and 0.0008 at 10 kHz, respectively. The dielectric tunability is about 10% at a dc bias field of 0.9 MV/cm.

Effect of BiFeO 3 addition on Bi 2O 3–ZnO–Nb 2O 5 based ceramics

In this paper, low temperature sintering of the Bi 2(Zn 1/3Nb 2/3) 2O 7 (β-BZN) dielectric ceramics was studied with the use of BiFeO 3 as a sintering aid. The effects of BiFeO 3 contents and the sintering temperature on the phase structure, density and dielectric properties were investigated. The results showed that the sintering temperature could be decreased and the dielectric properties could be retained by the addition of BiFeO 3. The structure of BiFeO 3 doped β-BZN was still the monoclinic pyrochlore phase. The sintering temperature of BiFeO 3 doped β-BZN ceramics was reduced from 1000 °C to 920 °C. In the case of 0.15 wt.% BiFeO 3 addition, the β-BZN ceramics sintered at 920 °C exhibited good dielectric properties, which were listed as follows: ε r = 79 and tan δ = 0.00086 at a frequency of 1 MHz. The obtained properties make this composition to be a good candidate for the LTCC application.

Enhancement of Pr 3+ luminescence in TeO 2–ZnO–Nb 2O 5–MoO 3 glasses containing silver nanoparticles

In this paper, we report the influence of silver nanoparticles (NPs) on the luminescence properties of TeO 2–ZnO–Nb 2O 5–MoO 3 glass doped with trivalent praseodymium (Pr 3+) ions. From the XRD, Raman and DTA measurements, glasses structural and thermal properties were determined. The experiments were performed with samples containing different concentrations of NPs controlled by heat-treatment of the glass. The enhancement of the Stokes luminescence with an increase of the NPs concentration was observed for these samples excited at 470 nm. The influence of the NPs on the frequency upconversion (anti-Stokes) emissions of Pr 3+ under excitation at 586 nm was also investigated, in resonance with the 3H 4→ 1D 2 transition. The excited Pr 3+ ions exchange energy in the presence of the nanoparticles, originating efficient conversion from orange to blue. The enhancement in the intensity of the luminescence at ∼493 nm, corresponding to the 3P 0→ 3H 4 transition, is due to the influence of the large local field on the Pr 3+ ions, which are located near the metallic nanoparticles.

Sintering behavior and microwave dielectric properties of Bi 2O 3–ZnO–Nb 2O 5-based ceramics sintered under air and N 2 atmosphere

The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi 2(Zn 1/3Nb 2/3) 2O 7 (BZN) and Bi 2(Zn 1/3Nb 2/3− x V x ) 2O 7 (BZNV, x = 0.001) sintered under air and N 2 atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V 2O 5 and N 2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N 2 atmosphere with ɛ r = 76.1, Q = 850 and Q f = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with ɛ r = 76.7, Q = 890 and Q f = 3580 GHz. The temperature coefficient of resonant frequency τ f was not obviously influenced by the different atmospheres. For BZN ceramics the τ f was −79.8 ppm/°C while τ f is −87.5 ppm/°C for BZNV ceramics.

Temperature-dependent dielectric, impedance and tunability studies on bismuth zinc niobate ((Bi 1.5Zn 0.5)(Nb 1.5Zn 0.5)O 7) ceramics

Bi 2O 3–ZnO–Nb 2O 5-based pyrochlore ceramics are receiving increasing attention due to their excellent dielectric properties in the microwave frequency range. Site disorder at the pyrochlore A-site is well known for lone pair active cations like Bi 3+ and is attributed as the reason for this material's high dielectric constant and tunability. Bismuth zinc niobate ((Bi 1.5Zn 0.5)(Nb 1.5Zn 0.5)O 7) [BZN] ceramics are prepared by the conventional solid-state reactions. The relative permittivity ( ɛ r) and the dielectric loss tangent (tan δ) of the BZN ceramics sintered at 1000 °C are found to be around 130 and 0.0004, respectively at a frequency of 1 MHz measured at room temperature. The impedance spectroscopy measurements are conducted at different temperatures to separate grain and grain boundary contributions to the dielectric constant. The tunability of these ceramics is studied under a constant dc bias voltage.

Second-order optical non-linearity initiated in Li 2O–Nb 2O 5–SiO 2 and Li 2O–ZnO–Nb 2O 5–SiO 2 glasses by formation of polar and centrosymmetric nanostructures

Amorphous nanoheterogeneities of the size less than 100 Å have been formed in glasses of the Li 2O–Nb 2O 5–SiO 2 (LNS) and Li 2O–ZnO–Nb 2O 5–SiO 2 (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher T g lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO 3 and non-polar LiZnNbO 4 in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO 3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO 4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO 3 crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.

High-permittivity and low-loss dielectric tunable pyrochlore thin films deposited by radio frequency magnetron sputtering from a lead zinc niobate target

Since Bi 2O 3–ZnO–Nb 2O 5 (BZN) pyrochlore thin films have been introduced as a tunable dielectric, the substitution of Bi with Pb could be a reasonable choice. The PbO–ZnO–Nb 2O 5 (PZN) cubic pyrochlore thin films were produced by radio frequency sputtering, and their dielectric properties, in terms of tunability, were measured. Up to 33.4% of tunability and comparable K factors with BZN films were obtained. The effects of film crystallization, along with substrate heating and post-annealing on the dielectric properties, were similar to those of BZN. However, strong texturing developed in the PbO–ZnO–Nb 2O 5 (PZN) films deposited at a high substrate temperature, which caused degradation of the loss tangent and K factor.

Silver cofirable Bi 1.5Zn 0.92Nb 1.5O 6.92 microwave ceramics containing CuO-based dopants

Bi 2O 3–ZnO–Nb 2O 5 system has emerged as a good low sintering (∼1050 °C) microwave material because it exhibits high dielectric constant and low temperature coefficient of resonance frequency ( τ f). We have lowered the sintering temperature of Bi 1.5Zn 0.92Nb 1.5O 6.92 (BZN) below 900 °C by using 3 wt.% of CuO-based dopants, such as 0.21BaCO 3–0.79CuO (BC) and 0.81MoO 3–0.19CuO (MC). The doped BZN exhibits high microwave dielectric constant at 2.3 GHz ( k ∼ 120). The interfacial behavior between BZN and silver was investigated by using X-ray diffractometer, scanning electronic microscope, and electronic probe microanalyzer. The extent of silver migration of MC and BC dopants is reduced at least by one order of magnitude as compared with V 2O 5 dopant when the samples was prepared at 900 °C for 4 h. Thus, CuO-based dopants can replace V 2O 5 to lower the sintering temperature of BZN and to be cofired with silver.

Low-sintering ceramic materials based on Bi 2O 3–ZnO–Nb 2O 5 compounds

In this work, sintering behaviour of Bi 2O 3–ZnO–Nb 2O 5 compounds was investigated in order to develop LTCC materials with suitable microwave properties. Structure, dielectric properties and sintering were studied for ceramic dielectrics based on the system: Bi 2ZnNb 2O 9 with the pyrochlore structure and ZnNb 2O 6 with a columbite one. The work was carried out over a wide range of initial components concentration. Ceramic samples of these materials were prepared by the mixed oxide technique. The effect of adding glass to the materials have been discussed. The sintering behaviour, dielectric permittivity, quality factor and crystal structures have been characterized for ceramic samples depending on compositions. Low-temperature co-firable ceramic material with ɛ ∼ 30, τ ɛ = 0 and Q × f = 3500 GHz based on the above system was synthesized.

Low-temperature firing and microwave dielectric properties of ZnO–Nb 2O 5–TiO 2–SnO 2 ceramics with CuO–V 2O 5

The effects of CuO–V 2O 5 addition on the sintering temperature and microwave dielectric properties of ZnO–Nb 2O 5–TiO 2–SnO 2 were investigated. The CuO–V 2O 5 addition lowered the sintering temperature of ZnO–Nb 2O 5–TiO 2–SnO 2 ceramics effectively from 1150 to 860 °C due to the liquid-phase effect of Cu 2V 2O 7 and Cu 3(VO 4) 2, as observed by XRD. The microwave dielectric properties were found to strongly correlate with the sintering temperature and the amount of CuO–V 2O 5 addition. The maximum Qf values decreased with increasing CuO–V 2O 5 content, due to the formation of the second phase, Cu 3(VO 4) 2 and CuNbO 3. Zero τ f value can be obtained by properly adjusting the sintering temperature. At 860 °C, ZnO–Nb 2O 5–TiO 2–SnO 2 ceramics with 1.5 wt.% CuO–V 2O 5 gave excellent microwave dielectric properties: ɛ r = 42.3, Qf = 9000 GHz and τ f = 8 ppm/°C.

Observations on structural evolution and dielectric properties of oxygen-deficient pyrochlores

Non-stoichiometric ceramics with the series oxygen-deficient pyrochlore in Bi 2O 3–ZnO–Nb 2O 5 ternary system was investigated to obtain structural information. Crystal structure and dielectric properties of the group of Bi 1.5−2 x Zn 1+2 x Nb 1.5O 7− x (with x=0–0.3) compositions have been studied. The compounds departured badly from stoichiomeric compositions lead to structural distortion and unbalance of pyrochlore phase, till secondary phase occurs for x=0.3. It can be inferred from Raman spectra that the concentration and ratio of species occupied B site is stable, while those of species occupied A site vary between the series compositions. It is reasonable to reckon that zinc dominantly occupies B site in pyrochlore structure with compositions varying. The experimental results show that dielectric constant ( ε) decrease linearly while the temperature coefficient of dielectric constant ( α ε ) effectively increases with increasing of the x-value. Crystal distortion and structural defect resulting from chemical composition unbalance bring on the change of dielectric properties for the small x-value.

Improvements of sintering and dielectric properties on Bi 2O 3–ZnO–Nb 2O 5 pyrochlore ceramics by V 2O 5 substitution

The effects of V 2O 5 on the phase formation and dielectric properties of Bi 2O 3–ZnO–Nb 2O 5 (BZN) pyrochlore ceramics were investigated. With the small amount of V 2O 5 substitution (0.005≤ x≤0.05), the sintering temperatures of Bi 1.5Zn 0.5(Zn 0.5Nb 1.5− x V x )O 7 can be effectively reduced from 1000 to 840 °C while the phase structures still kept to be the pure cubic pyrochlores. The V 2O 5 seems to provide an eutectic melt below the sintering temperature to improve the sinterability. The dielectric constants decrease gradually with V 2O 5 substitution while the temperature coefficients of the samples continuously increase. The dielectric loss are in same level as that of the basic composition at the smaller substitute amount ( x≤0.02) but then degraded in lower frequency when the substitution reached to x=0.05. Obvious dispersion in the dielectric constant and loss was observed as a function of frequency and temperature after the substitution.

Mn 4+ and W 6+ substitution on Bi 2O 3–ZnO–Nb 2O 5-based low firing ceramics

The ion substitution with Mn 4+ and W 6+ co-substituted Nb 5+ in B site of a low firing Bi 2O 3–ZnO–Nb 2O 5-based A 2B 2O 7 pyrochlore ceramics was investigated. The Mn 4+ and W 6+ co-substitution was tentatively introduced in cubic-monoclinic pyrochlores co-existing ceramics Bi 3 x Zn 2−3 x (Zn x Nb 2− x−2 y Mn y W y )O 7 ( x=0.5–0.65, y=0, 0.02, 0.05, 0.1) and the results shows interested regular influence on the structure, dielectric properties with the amount of substitution amount change. With the structure evaluation and electrical properties measurement results, the Mn 4+ and W 6+ substituted Nb 5+ in B site shows effective to depress the grain growth and the ceramic with fine grains in 1–3 μm can be obtained. The electrical properties was also enhanced in smaller substitution amount but degraded with the substitution amount increasing. Based on these results, small amount of Mn 4+ and W 6+ substitution was successfully applied to a base ceramic with the electrical properties satisfied the NP0 specification to miniaturize the grains and enhance the sintering behavior.

Optical bistability for ZnO–Nb2O5–TeO2 glasses

Abstract We examined the optical nonlinear properties of ZnO–Nb 2 O 5 –TeO 2 . The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ (3) is about 1.0 × 10 −12 esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.