Zinc Niobate Research Articles

Microwave dielectric and Raman scattering studies on bismuth zinc niobate thin films

Bismuth zinc niobate (Bi1.5Zn1.0Nb1.5O7) thin films were deposited on fused silica substrates by pulsed laser deposition. Its phase composition and microstructure were characterized by x-ray diffraction and atomic force microscopy. The as deposited films were amorphous and all of them were crystallized after a postdeposition annealing at 600 °C for 30 min in air. The crystallite size of the films was found to be varying between 31 and 60 nm with respect to the oxygen pressure in the deposition chamber. The films were found to be less oriented with the decreasing crystallite size. The films deposited under different oxygen pressures showed a microwave dielectric permittivity in between 98–124 and a loss tangent in between 0.005 and 0.007 over the X-band frequency range. From the Raman scattering data of the bulk and thin films, it was found that the Raman modes in thin films are relatively more intense and additional Raman modes were appearing in the films in the low frequency range, which reveal that the local symmetry in the films is different from that of the bulk. The variations in the microwave dielectric properties due to processing can be attributed to the change in the local symmetry of the film.

Effect of process parameters and post-deposition annealing on the microwave dielectric and optical properties of pulsed laser deposited Bi1.5Zn1.0Nb1.5O7 thin films

Bismuth Zinc niobate (Bi1.5Zn1.0Nb1.5O7) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures. The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53 (at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11 at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase in band gap, refractive index and microwave dielectric constant.

LPG Sensing of Nanostructured Zinc Oxide and Zinc Niobate

LPG Sensing of Nanostructured Zinc Oxide and Zinc Niobate

Low-Temperature Synthesis and Characterization of Lead Zinc Niobate Thick Films

Perovskite Pb(Zn 1/3 Nb 2/3 )Ο 3 (PZN) thick films were prepared by a hydrothermal route at a low temperature (150°C) on Ti metal, where the titanium (Ti) metal served as both the substrate and bottom electrode for the PZN films. The thickness of the PZN film fabricated on the Ti substrate was about 20 μm. We have demonstrated that the concentration of KOH plays a key role in obtaining the perovskite structure in the PZN film. The dielectric relaxation was studied as a function of temperature and frequency. A dispersion of the maximum dielectric permittivity (E max ) appears around the temperature of T m , which shifts toward higher temperatures with increasing frequency. The variation of T m with frequency follows the Vogel-Fulcher relationship. The variation of 1/e with temperature above T m deviates from the Curie-Weiss (CW) law but satisfies the modified CW law. The relaxation indication coefficient (γ) and broadening parameter (A) were estimated from a quadratic fit of the modified Curie-Weiss law and were found to be 2.00 and 42 K, respectively, indicating strong relaxor behavior. The samples showed excellent reproducibility in the measurements of leakage current, a remnant polarization of 14 μC/cm 2 , and a coercive field of 300 kV/m.

Piezoelectric Properties of PZT‐Based Ceramic with Highly Aligned Pores

Porous lead zirconate titanate–lead zinc niobate (PZT–PZN) piezoelectric ceramics with a high degree of pore alignment were fabricated using directional freeze casting of a ceramic/camphene slurry. Well‐aligned pores were formed as the replica of the camphene dendrites that grew in a preferential orientation, while a high porosity of 90% was achieved by employing a low initial solid loading of 5 vol%. As the orientation angle of the pores to the poling direction was decreased, the hydrostatic piezoelectric properties, such as hydrostatic piezoelectric strain coefficient (dh), the hydrostatic piezoelectric voltage coefficient (gh), and the hydrostatic figure of merit, increased significantly. The sample containing pores aligned parallel to the poling direction showed an extremely high HFOM of 161019 × 10−15 Pa−1, which was ∼1300 times higher than that (124 × 10−15 Pa−1) of the dense sample, owing to the presence of aligned pores.

Different models for the polar nanodomain structure of PZN and other relaxor ferroelectrics

Computer simulations have been carried out to test the recently proposed model for the nanodomain structure of relaxor ferroelectrics such as lead zinc niobate (PZN). In this recent model it was supposed that the polar nanodomains are three-dimensional, that the observed diffuse rods of scattering originate from the boundaries between domains and that the Pb displacements may be directed along \langle {100} \rangle, \langle {111} \rangle or \langle {110} \rangle. This is in marked contrast to a previously published model, which described the polar domains as thin plates with Pb displacements confined to the \langle {110} \rangle directions within the essentially two-dimensional domains. The present results confirm that \langle {100} \rangle and \langle {111} \rangle types of Pb displacement are viable possibilities, but the number of domain boundaries required to produce sufficiently strong diffuse rods of scattering means that individual domains cannot be described as three-dimensional and must still be relatively thin. The current work has been carried out with no direct involvement of theB-site cation ordering, which many workers assume is necessary to understand the formation of the polar nanodomains. While it may be true that theB-site cation distribution could provide an underlying perturbation field that might ultimately limit the extent of any polar domain, it is certainly not necessary to produce the observed scattering effects.

Monoclinic PZN-8%PT [Pb(Zn0.3066Nb0.6133Ti0.08)O3] at 4 K

The structure of the relaxor ferroelectric Pb(Zn(0.3066)Nb(0.6133)Ti(0.08))O(3) (lead zinc niobium titanium trioxide), known as PZN-8%PT, was determined at 4 K from very high resolution neutron powder diffraction data. The material is known for its extraordinary piezoelectric properties, which are closely linked to the structure. Pseudo-cubic lattice parameters have led to considerable controversy over the symmetry of the structure. We find the structure to be monoclinic in the space group Cm (No. 8), with the Zn, Nb and Ti cations sharing the octahedrally coordinated B site (site symmetry m, special position 2a) and Pb occupying the 12-coordinate A site (site symmetry m, special position 2a). O atoms occupy a disorted octahedron around the B site (site symmetry m and special position 2a, and site symmetry 1 and general position 4b). Atomic coordinates have been determined for the first time, allowing the direction of spontaneous polarization to be visualized.

Temperature and electric field dependence of ultrasonic wave propagation and attenuation in PZN-PT single crystal in vicinity of a phase transition

The longitudinal and transverse modes of ultrasound propagation in Lead Zinc Niobate–Lead Titanate (PZN–PT) single crystal solid solutions are investigated as a function of temperature. The influence of an electric DC bias field on the elastic stiffness at various temperatures is studied. The presence of more stable phases induced by this electric field is observed. The polarization directions are modeled in terms of free energy function. The experiments are conducted in a dedicated temperature chamber working in a wide temperature range from 200 up to 470 K for ultrasonic measurements thin plate samples with the option for DC bias fields. The bias field was applied by a high voltage amplifier Trek model 610D. Crystal cuts of [001], [110] and [111] were used for the study of electric field poling conditions and temperature influence on structure induced by polarization orientation. A study of anomalies in sound velocity and relative attenuation near ferroelectric transitions is performed. It is well established that near the temperature of a second-order structural phase transitions, and in particular near the Curie point of ferroelectrics, anomalously strong ultrasonic absorption occurs.

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.

Preparation of Highly Dense PZN–PZT Thick Films by the Aerosol Deposition Method Using Excess‐PbO Powder

Lead zinc niobate–lead zirconate titanate thick films with a thickness of 50–100 μm were deposited on silicon and alumina substrates using the aerosol deposition method. The effects of excess lead oxide (PbO) on stress relaxation during postannealing were studied. Excess PbO content was varied from 0 to 5 mol%. The as‐deposited film had a fairly dense microstructure with nanosized grains. The films deposited on silicon were annealed at temperatures of 700°C, and the films deposited on sapphire were annealed at 900°C in an electrical furnace. The annealed film was detached and cracks were generated due to the high residual compressive stress and thermal stress induced by thermal expansion coefficient mismatch. However, the film deposited using powder containing 2% of excess PbO showed no cracking or detachment from the substrate after the postannealing process. The PbO evaporation at elevated temperature during the postannealing process seemed to have reduced the residual compressive stress. The remanent polarization and relative dielectric constant of the 50 μm thick films annealed at 900°C were 43.1 μC/cm2 and 1400, respectively, which were comparable with the values of a bulk specimen prepared by a powder sintering process.

Giant Permittivity of a Bismuth Zinc Niobate–Silver Composite

Bismuth zinc niobate–Silver (BZN–Ag) composites were prepared by the solid‐state ceramic route. The sintering temperature of BZN–Ag composites was lowered to 850°C/2 h. The structure and surface morphology of the composites were investigated using X‐ray diffraction and optical microscope. The dielectric and conducting properties of the composites were systematically investigated with the volume fraction of silver in the frequency range from 1 KHz to 1 MHz. The dielectric constant of the composite increases with the silver content and is in good agreement with the power law below the percolation limit. Addition of 0.14 volume fraction of silver increases the dielectric constant of BZN+2 wt% B2O3 from 150 to 2350 at 1 MHz. However, 15 volume percentage of silver loading results in a large permittivity of (ɛr)≈105 with a low dielectric loss (tan δ≈10−2) at 1 MHz. Subsequent increase in silver loading decreases the dielectric constant. The BZN–B2O3–Ag composite with large permittivity may find applications in electromechanical and tunable devices.

Synthesis and characterization of bismuth zinc niobate pyrochlore nanopowders

Bismuth zinc niobate pyrochlores Bi1.5ZnNb1.5O7 (alpha-BZN), and Bi2(Zn1/3Nb2/3)2O 7 (beta-BZN) have been synthesized by chemical method based on the polymeric precursors. The pyrochlore phase was investigated by differential scanning calorimetry, infrared spectroscopy, and X ray diffraction. Powder and sintered pellets morphology was examined by scanning electron microscopy. The study of alpha-BZN phase formation reveals that, at 500 °C, the pyrochlore phase was already present while a single-phased nanopowder was obtained after calcination at 700 °C. The crystallization mechanism of the beta-BZN is quite different, occurring through the crystallization of alpha-BZN and BiNbO4 intermediary phases. Both compositions yielded soft agglomerated powders. alpha-BZN pellets, sintered at 800 °C for 2 hours, presented a relative density of 97.3% while those of beta-BZN, sintered at 900 °C for 2 hours, reached only 91.8%. Dielectric constant and dielectric loss, measured at 1 MHz, were 150 and 4 x/10-4 for a-BZN, and 97 and 8 x 10-4 for beta-BZN.

Effects of Pb(Zn1∕3Nb2∕3)O3 addition and postannealing temperature on the electrical properties of Pb(ZrxTi1−x)O3 thick films prepared by aerosol deposition method

Effects of the lead zinc niobate (PZN) addition and postannealing temperature on the electrical properties of the lead zirconate titanate (PZT) films were observed to improve electrical properties of the PZT film. The PZN content was varied from 0% to 40%, and the postannealing temperature was varied from 500to900°C. The as-deposited film had a fairly dense microstructure without any cracking and showed a single perovskite phase formed with nanosized grains. Meanwhile, rapid grain growth was observed when the postannealing temperature was increased from 700to900°C. The PZN-added PZT film showed poorer electrical properties than the pure PZT film did when the films were annealed at 700°C but higher remnant polarization, dielectric constant, and piezoelectric response when the films were annealed at 900°C. Remnant polarization value, relative dielectric constant, and piezoelectric constant of the 20% PZN-added PZT films annealed at 900°C were 50.0μC∕cm2, 1643, and 200pC∕N, respectively, which are values sufficiently high to be comparable with the bulk specimen sintered at 1200°C.

Microstructure and dielectric properties of pyrochlore Bi2Ti2O7 thin films

Bi 2 Ti 2 O 7 thin films were grown by radio-frequency magnetron sputtering on bare and Pt-coated sapphire substrates at low substrate temperatures (∼200 °C). Postdeposition anneals were carried out at different temperatures to crystallize the films. Nearly phase-pure Bi2Ti2O7 thin films with the cubic pyrochlore structure were obtained at annealing temperatures up to 800 °C. Impurity phases, in particular Bi4Ti3O12, formed at higher temperatures. At 1 MHz, the dielectric constants were about 140–150 with a very small tunability and the dielectric loss was about 4×10−3. The dielectric loss increased with frequency. The dielectric properties of Bi2Ti2O7 films are compared to those of pyrochlore bismuth zinc niobate films.

Effects of strontium on the characteristics of Pb(Zr1/2Ti1/2)O3--Pb(Zn1/3Nb2/3)O3 ceramics

The dielectric and piezoelectric properties of pyrochlore-free lead zirconate titanate-lead zinc niobate ceramics were investigated systematically as a function of Sr doping. The powders of Pb(1− x )Sr x [0.7(Zr1 / 2Ti1 / 2)–0.3(Zn1 / 3Nb2 / 3)]O3, where x = 0–0.06 were prepared using the columbite-(wolframite) precursor method. The ceramic materials were characterized using X-ray diffraction, dielectric spectra, hysteresis and electromechanical measurements. The phase-pure perovskite phase of Sr-doped PZN--PZT ceramics was obtained over a wide compositional range. The results showed that the optimized electrical properties were also achieved at composition x = 0.0, which were K P = 0.69, d 33 = 670 pC N−1, P r = 31.9 µC cm−2 and εrmax = 18600. Maximum dielectric constant values of the systems decreased rapidly with increasing Sr concentration. Moreover, with increasing Sr concentration dielectric constant versus temperature curves become gradually broader. The diffuseness parameter increased significantly with Sr doping. Furthermore, Sr doping has been shown to produce a linear reduction in the transition temperature (T m) = 294.1–12.7x°C with concentration (x). Sr shifts the transition temperature of this system at a rate of 12.7°C mol−1%.

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.

Fabrication of Porous PZT–PZN Piezoelectric Ceramics With High Hydrostatic Figure of Merits Using Camphene‐Based Freeze Casting

Porous lead zirconate titanate–lead zinc niobate (PZT–PZN) piezoelectric ceramics with interconnected pore channels were fabricated using the camphene‐based freeze‐casting method. In this method, warm PZT–PZN/camphene slurries with various solid loadings (10, 15, 20, and 25 vol%) were prepared by ball milling at 60°C and then cast into molds at 20°C, resulting in the formation of solidified green bodies comprised of three‐dimensionally interconnected camphene dendrite networks and concentrated ceramic particle walls. After the removal of the frozen camphene via sublimation, the samples were sintered at 1200°C for 2 h. All of the fabricated samples showed highly porous structures, consisting of fully dense PZT–PZN walls without defects, such as cracks or pores. As the initial solid loading was decreased from 25 to 10 vol%, the porosity was linearly increased from 50% to 82%. This increase in the porosity led to a reduction in the permittivity, a moderate decline in the d33 value, and a rapid decline in the d31 value, which endowed the porous samples with a high hydrostatic figure of merit (HFOM). The highest HFOM value of 35650 × 10−15 Pa−1 was achieved for the sample with a porosity of 82%, as well as ɛ33=284, dh=298 pC/N, and gh=118 × 10−3 V·(m·Pa)−1.

Electrical Properties of Lead Zinc Niobate - Lead Zirconate Titanate Thick Films Formed by Aerosol Deposition Process

Lead zinc niobate (PZN) added lead zirconate titanate (PZT) thick films with thickness of 5~10 μm were fabricated on silicon and sapphire substrates using aerosol deposition method. The contents of PZN were varied from 0, 20 and 40 %. The as deposited film had fairly dense microstructure without any crack, and showed only a perovskite single phase formed with nano-sized grains. The as-deposited films on silicon were annealed at temperatures of 700oC, and the films deposited on sapphire were annealed at 900oC in the electrical furnace. The effects of PZN addition on the microstructural evolution were observed using FE-SEM and HR-TEM, and dielectric and ferroelectric properties of the films were characterized using impedance analyzer and Sawyer-Tower circuit, respectively. The PZN added PZT film showed poor electrical properties than pure PZT film when the films were coated on silicon substrate and annealed at 700oC, on the other hand, the PZN added PZT film showed higher remanent polarization and dielectric constant values then pure PZT film when the films were coated on sapphire and annealed at 900oC. The ferroelectric and dielectric characteristics of 20% PZN added PZT films annealed at 900oC were comparable with the values obtained from bulk ceramic specimen with same composition sintered at 1200oC.

Preparation of zinc-containing thin coatings on LiNbO3 substrates

Zinc oxide thin films are prepared on LiNbO3 single-crystal substrates with the preliminary deposition of a buffer layer consisting of zinc niobate of the composition ZnNb2O6 with an orthorhombic crystal lattice or the composition Zn3Nb2O8 with a monoclinic crystal lattice. The phase composition, the thickness, and the quality of the films are characterized using X-ray powder diffraction and electron microscopy.

Low-voltage and high-tunability interdigital capacitors employing lead zinc niobate thin films

Employing high-tunability PbO–ZnO–Nb2O5 thin film dielectrics, low-voltage and high-tunability interdigital capacitors (IDCs) were implemented on a silicon substrate. In order to reduce the bias voltage of the IDC and increase its tunability, its electrodes were fully embedded into the thin film dielectrics to confine fringing electric fields within them. At 4V, the tunability of the IDCs was analyzed in terms of the electrode width and spacing by measuring reflection coefficients at 1GHz. The fabricated IDC with width and spacing of 1.5 and 1.8μm, respectively, achieved tunability of 26% and a Q factor of 10 at 5.5V.