O3 Microwave Research Articles

Sintering behavior and dielectric properties of Bi3+-substituted Nd(Zn0.5Ti0.5)O3microwave ceramics

The sintering behavior and dielectric properties of Bi[Formula: see text]-substituted Nd(Zn[Formula: see text]Ti[Formula: see text]O3(abbreviated as NZT) microwave ceramics (Nd[Formula: see text]Bi[Formula: see text])(Zn[Formula: see text]Ti[Formula: see text])O3[Formula: see text] (abbreviated as NBZT) are investigated. XRD results reveal the formation of single perovskite solid solutions for [Formula: see text] samples. For [Formula: see text] samples, pyrochlore phase begins to segregate from the perovskite phase and its volume fraction increases with [Formula: see text]. B-site Zn[Formula: see text]/Ti[Formula: see text] 1:1 long range order (LRO) is detected by Raman Spectroscopy. The degree of LRO varies as a function of sintering conditions and chemical composition. The microwave dielectric properties of the composition are measured. By substituting Bi[Formula: see text] for Nd[Formula: see text], the temperature coefficient of resonant frequency [Formula: see text] tunes toward zero, however, the microwave quality factor, [Formula: see text] deteriorates. For [Formula: see text], [Formula: see text] reaches a minimum value of [Formula: see text] with relative permittivity of [Formula: see text] and [Formula: see text], respectively. The effect of Bi-doping on the [Formula: see text] value is discussed.

Structure and microwave dielectric properties of Ca0.66La0.387Ti0.88O3 ceramics

Ca0.66La0.387Ti0.88O3 microwave dielectric ceramics were prepared via a mixed oxide solid state sintering route and characterized. X-ray diffraction revealed the formation of single phase Ca0.66La0.387Ti0.88O3 ceramics with orthorhombic (Pbnm) symmetry within the detection limit of the in-house XRD facility. Raman spectroscopy revealed the presence of seven Raman active bands evident of orthorhombic symmetry, in agreement with the present X-ray diffraction results. The microstructure of sintered samples appeared almost dense with some occasional pores. Ca0.66La0.387Ti0.88O3 exhibited reasonable relative permittivity (~71.5) and quality factor (~13,407 GHz); however, its temperature coefficient of resonance frequency was high (~136.4 × 10−6/°C) for commercial applications and requires further optimization.

Effects of BaWO4 additive on Raman phonon modes and structure–property relationship of Ba(Mg1/3Ta2/3)O3 microwave dielectric ceramics

Ba(Mg1/3Ta2/3)O3–BaWO4 (BMT–BW) microwave dielectric ceramics were synthesized using the conventional solid-state sintering technique. Effects of BW additive on Raman phonon modes and structure–property relationship of BMT ceramics were evaluated. The results show that increasing BW contents affect the crystal structures and dielectric properties of BMT ceramics greatly. The lattice parameters (a, c) gradually decrease with the increasing of W6+ content; the lattice parameter ratio (c/a) and the ordering degree reach a maximum value at x=0.04, and then gradually decrease with W6+ concentration. Studies about Raman spectra show that the peak frequencies of A1g(O) modes near 795cm−1 and Eg(O) modes near 158cm−1 and 430cm−1 reach a maximum value at x=0.04; the peak frequencies of Eg(Ta) modes near 210cm−1 reach a minimum value at x=0.04. The relationship between crystal structures and dielectric properties were finally established with vibration modes as the media.

Low loss (Ba1−xSrx)(Co1/3Nb2/3)O3 solid solution: phase evolution, microstructure and microwave dielectric properties

(Ba1−xSrx)(Co1/3Nb2/3)O3 (0 ≤ x ≤ 0.5) microwave dielectric ceramics had been prepared using the solid-state reaction method. The dense microstructures with small grains were obtained. All Sr2+ substituted samples exhibited the perovskite phase. The structure transition from cubic to hexagonal occurred with the increase of x, which led to higher degree of 1:2 ordered structure in the B site. The improved Q × f value was correlated monotonously with the ordering parameters S. The dielectric constant (e r ) and the temperature coefficient of resonant frequency (τ f ) could be effectively tuned by tailoring x. A good combination of microwave dielectric properties was obtained for (Ba0.95Sr0.05)(Co1/3Nb2/3)O3 sintered at 1380 °C: e r = 33.3, Q × f = 87,120 GHz, τ f = 4 ppm/°C.

Ba[Mg<sub>(1-</sub><italic><sub>x</sub></italic><sub>)/3</sub>Zr<italic><sub>x</sub></italic>Nb<sub>2(1-</sub><italic><sub>x</sub></italic><sub>)/3</sub>]O<sub>3</sub>微波介质陶瓷的红外光谱

Ba[Mg(1- x )/3Zr x Nb2(1- x )/3]O3 (BMZN, x =0, 0.10, 0.15) microwave dielectric ceramics were synthesized at 1520℃ using the conventional solid-state sintering technique. Effect of Zr4+ substitution on crystal structures and dielectric properties of the BMZN ceramics was studied by far-infrared spectroscopy (FIR). The results show that with increasing Zr4+ concentration the IR active modes near 370 cm-1 split and new phonon modes appear; the IR active modes near 410 cm-1 disappear; the frequencies of the IR active modes near 230, 290 and 540 cm-1 shift towards high frequency and the intensities of these modes decrease. Studies about the FIR spectra show that with increasing Zr4+ concentration the crystal structures of the BMZN ceramics transformed from hexagonal to cubic structure. The correlations between dielectric properties and IR modes were established with vibration modes as the media.

Influences of B-site Cations on Intrinsic Dielectric Properties of Ba(B′1/3B′′2/3)O3 Materials

Effects of B-site cations on polar phonon frequencies, mode effective charges, and lattice dielectric response of 1:2 ordered Ba(Mg1/3Ta2/3)O3, Ba(Mg1/3Nb2/3)O3, and Ba(Zn1/3Nb2/3)O3 microwave dielectrics are studied using first-principles calculations. The calculated optical phonon frequencies and the average dielectric constants are found to be in excellent agreement with experiments. Replacing Ta (Mg) with Nb (Zn) is found to significantly affect frequency, oscillator strength, and mode effective charges of the dominant polar phonons. Dielectric contributions from O anions are dominant and strongly B-site dependent. Furthermore, we demonstrate that the greater the dielectric contribution from O anions, the smaller the measured microwave Q × f-factor.

First-principle calculation and assignment for vibrational spectra of Ba(Mg1/3Nb2/3)O3 microwave dielectric ceramic

1:2 B-site cation ordered Ba(Mg1/3Nb2/3)O3 ceramic was synthesized using conventional solid-state reaction at 1600 °C for 12 h. The structure parameters were obtained through Rietveld refinement of X-ray diffraction data. The Raman peak frequencies were obtained by Lorenz fitting on Raman spectrum. Four-parameter semiquantum model was used to fit the infrared (IR) reflectivity spectrum, and the fitted parameters were used to calculate the dielectric permittivity ε and dielectric loss tanδ. A total of 9 active Raman and 16 active IR modes were obtained using first-principle calculations based on density functional theory with local density approximation. All of the vibrational modes were assigned and represented by linear combinations of the symmetry coordinates deduced using group theory analysis. The Raman mode with the highest frequency A1g(4) (789 cm−1) can be described as the breathing vibration of NbO6. The IR modes Eu(1) (149 cm−1) and A2u(2) (212 cm−1), which can be described as the twisting vibrations of Ba–MgO6/Ba–NbO6 on the a–b plane and the stretching vibrations of Ba–MgO6/Ba–NbO6 along the c direction, respectively, are the dominant contributing modes to ε and tanδ. The dielectric property parameters obtained using IR spectrum fittings, first-principal calculations, and microwave measurements were compared.

Aqueous processing and effects of V2O5 on microwave dielectric properties of multilayer Li1.075Nb0.625Ti0.45O3 ceramics

In the present work, we report the development of an aqueous tape casting method and a low temperature co-firing process for fabrication of multilayer Li1.075Nb0.625Ti0.45O3 microwave dielectric ceramics. A co-binder, consisting of polyvinyl acetate latex (PVAc) and polyvinyl alcohol (PVA), was used to prepare aqueous Li1.075Nb0.625Ti0.45O3 tapes. PVA addition increased the tape flexibility and adhesiveness but resulted in decreased tensile strength. Rheological tests indicated that the aqueous ceramic slurry exhibited a typical shear thinning behavior without thixotropy, suitable for tape casting. Scanning electron microscopy (SEM) studies revealed that the green tapes have a defect-free surface and that the multilayer ceramics sintered at 900°C have a fine plate like, grainy microstructure of uniform size. At lower temperatures, increased densification rates were achieved by addition of V2O5 to Li1.075Nb0.625Ti0.45O3 ceramics. The saturated bulk densities and dielectric constants (ɛr) of Li1.075Nb0.625Ti0.45O3 multilayer ceramics affected by lower sintering temperatures with an increase in V2O5 doping, and then an improvement in the quality factor (Q × f value) of the samples was achieved at the lower sintering temperatures. As a result, the ɛr of 64.9 and the Q × f value of 8800 GHz were obtained in the sample with an addition of 3 wt.% V2O5, sintered at a temperature of 900°C. No reaction was observed between the ceramic and silver layers when sliver inner-electrode, was sintered with ceramic tapes at 900°C.

Long range B-site cation ordering and Briet–Wigner–Fano line shape of A1g-like Raman mode in Nd1−xSmx(Mg0.5Ti0.5)O3 microwave dielectric ceramics

Nd1−xSmx(Mg0.5Ti0.5)O3 (x=0.0–1.0) samples were prepared by solid-state reaction method. Rietveld refinement of X-ray diffraction data was done using P21/n space group with monoclinic symmetry, which supports 1:1 B-site cation ordering. Long range ordering (LRO) parameter decreased up to x=0.5 and then found to increase with further increase in Sm concentration. The A1g-like mode in Raman spectra was observed to possess Briet–Wigner–Fano line shape. The variation in obtained line width of the A1g-like mode supported LRO. Microwave dielectric characteristics such as dielectric constant (ɛr), quality factor (Q) and temperature coefficient of resonant frequency (τf) were measured in the range of 7–9GHz. ɛr decreased from 26.5 to 24.9 and τf become less negative from −58ppm/°C to −36ppm/°C with increase in Sm concentration. Q×f decreased from 47,500GHz (for x=0) to 39,800GHz (for x=0.5) and then increased to 44,600GHz (for x=1).

Textured Li0.95Nb0.45Ti0.7O3 Microwave Ceramics with Continuously Tunable Dielectric Properties

Textured Li0.95Nb0.45Ti0.7O3 (LNT) microwave dielectric ceramics were fabricated by the screen-printing templated grain growth technique (sp-TGG). The plate-like LNT particles with diameters of 5–20 μm and thicknesses of 0.5–2.0 μm prepared by molten salt synthesis (MSS) were chosen as templates. The <110> oriented LNT ceramics with an orientation degree of 73% were fabricated via the sp-TGG method. The dielectric anisotropy was observed in LNT(//) and LNT(⊥) samples. At microwave frequency, the LNT(//) sample exhibits ϵ r = 47, Q×f = 9893 GHz, τ f = −18 ppm/°C, whereas the LNT(⊥) sample exhibits ϵ r = 75, Q×f = 6942 GHz, τ f = 52 ppm/°C.

Effect of V2O5 on the aqueous tape casting of Li1.075Nb0.625Ti0.45O3 microwave ceramic

The effect of V2O5 addition on the aqueous tape casting of Li1.075Nb0.625Ti0.45O3 microwave ceramics has been investigated. The isoelectric point of the ceramic particles moved slightly toward more acid region after the dispersant absorbed on the particles, while the zeta potential increased significantly. The rheological test indicated that the ceramic slurry exhibited a typical pseudoplastic behavior without thixotropy and the addition of V2O5 increased the viscosity of the slurries. It is found that doping of V2O5 can improve the densification of Li1.075Nb0.625Ti0.45O3 green tapes. Due to the liquid phase effect of V2O5 addition, Li1.075Nb0.625Ti0.45O3 ceramic could be sintered at 900°C. A secondary phase was observed at the level of 3 wt% V2O5 addition. The addition of V2O5 does not induce much degradation on the microwave dielectric properties. In the case of 2 wt% V2O5 addition, the ceramics show good microwave dielectric properties of ɛr = 65, Q×f = 6350GHz. It represents that the ceramics could be promising for multilayer low-temperature co-fired ceramics (LTCC) application.

Production of Ba(Zn1/3Nb2/3)O3 ceramic by coprecipitation

Abstract A simple coprecipitation technique was successfully applied for the preparation of pure, nanosized, single phase Ba(Zn1/3Nb2/3)O3 microwave dielectric ceramic powders. Barium, zinc and niobium ions were precipitated as hydroxide under basic conditions using aqueous sodium hydroxide solution and single phase Ba(Zn1/3Nb2/3)O3 ceramic was produced at 800 °C. TEM revealed an average particle size of around 100 nm for the calcined powders. The samples sintered at 1250 °C for 4 h had a relatively high density and fine grain sizes. While the dielectric constant of ceramics varied between 37.5 and 39.8 the dielectric losses were lower than 4 × 10− 3 at frequency range of 1 kHz–2 MHz between 20 and 200 °C.

Anisotropic Dielectric Properties of LiNb0.6Ti0.5O3 Microwave Ceramics by Screen-Printing Templated Grain Growth

In this work, anisotropic LiNb0.6Ti0.5O3 (LNT) template particles are prepared by molten salt synthesis in LiCl flux. Plate-like particles with diameters of 5–20 μm and thicknesses of 0.5–2.0 μm synthesized at 1000°C are chosen as templates. Highly textured microwave ceramics of M-phase LNT with tunable dielectric properties are fabricated by a novel screen-printing templated grain growth technique (sp-TGG), and their characteristics and dielectric properties are studied systematically. Dielectric anisotropy is observed in dielectric constant (εr) and the temperature coefficient of dielectric constant (τε) at 1 MHz. LNT(//) samples exhibit lower εr (=55.3) than randomly oriented ceramics and a positive temperature coefficient τε (75 ppm/°C), whereas, LNT(⊥) samples exhibit higher εr (=83.6) and a negative temperature coefficient τε (= −120 ppm/°C). The textured ceramics also exhibit anisotropic and excellent properties at microwave frequency, with LNT-M(//) showing εr = 57.9, Q × f = 6325 GHz, τf = −14 ppm/°C and LNT-M(⊥) showing εr = 81.8, Q × f = 5751 GHz, τf = 43 ppm/°C. By tailoring along different directions, continuously tunable dielectric constant ranging from 55 to 83 could be obtained, and τf could be changed from −14 to 43 ppm/°C. These findings can be technologically beneficial for wireless communication devices.

Effect of sputtering power on microstructure of dielectric ceramic thin films by RF magnetron sputtering method using (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 as target

Radio frequency (RF) magnetron sputtering method was applied to prepare dielectric ceramic thin films on SiO2 (110) substrates using (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 microwave dielectric ceramics as target. The samples were deposited at different sputtering powers in Ar atmosphere. In particular, the microstructure and morphology of the thin films were investigated as a function of sputtering powers by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The results show that the thin films are polycrystalline and the sputtering power significantly influences the surface morphology and microstructure of the thin films. On increasing the sputtering power, the crystallinity improves and the grain size and roughness of the thin films reach maximum values at 200 W.

Fabrication of thin films by sputtering deposition using (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 ceramic as target

Dielectric ceramic thin films were fabricated on SiO2 (110) substrates by the radio frequency (RF) magnetron sputtering method using (Ba0.3Sr0.7)(Zn1/3Nb2/3)O3 microwave dielectric ceramic as target. The microstructure, components, and morphology of the thin films were investigated thoroughly. The results reveal that the experimental conditions can affect the growth of the thin films significantly. The main phases of the thin films are Ba0.5Sr0.5Nb2O6 and Ba0.27Sr0.75Nb2O5.78, which are of different composition from that of the ceramic target due to Zn loss. The thin films are polycrystalline with high-quality crystalline and are made up of dense rod-like structures. The growth mechanism of the thin films is discussed in particular.

Cation Ordering and Domain Boundaries in Ca[(Mg1/3Ta2/3)1−xTix]O3Microwave Dielectric Ceramics

Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1−xTix]O3 (x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111)c plane with a projected displacement vector in the 〈001〉c direction and ferroelastic domain boundaries parallel to the 〈100〉c direction.

Raman Spectroscopy of (Ba1-xSrx)(Mg1/3Nb2/3)O3Solid Solutions from Microwave-Hydrothermal Powders

Microwave-hydrothermal synthesis was employed to produce crystalline, single-phase Ba(Mg1/3Nb2/3)O3 and Sr(Mg1/3Nb2/3)O3 powders for the first time. The ceramics were mixed and fired at high temperatures to achieve ordered solid solutions. X-ray diffraction and Raman spectroscopy were employed to evaluate the crystal structure and phonon modes of chemically substituted (Ba1-xSrx)(Mg1/3Nb2/3)O3 (x = 0.0, 0.3, 0.5, 0.7, 0.9, 1.0) microwave ceramics. It was verified that these materials present a phase transition for Sr-rich samples (x ≥ 0.7), from trigonal to monoclinic . Lorentzian lines were used to fit the spectra obtained at low temperatures, which present 35 bands for the Sr(Mg1/3Nb2/3)O3 ceramic. The position and width of the phonon modes were determined and correlated to the ionic radii, mass, and tolerance factors for the different atoms substituted in the A-site.

Structure and Dielectric Behavior of the (1−x)La(Mg1/2Ti1/2)O3 < eqid1 > xBa(Mg1/2W1/2)O3 Microwave Ceramics

The sequence of structure transformations, P2 1 /n − I2/m − Fmm, involving oxygen octahedral tilting has been revealed in the ceramics of the whole-range B-site ordered perovskite system (1−x)La(Mg 1/2 Ti 1/2 )O 3 −xBa(Mg 1/2 W 1/2 )O 3 . Microwave dielectric characteristics of the ceramics have been evaluated as a function of their composition. The observed structure sequence and structure-dependent dielectric behavior are discussed in respect to an order of the transition between anti-phase tilted and untilted configurations as well as a likely clustering in the system.

Influence of Non‐Stoichiometry on the Structure and Properties of Ba(Zn1/3Nb2/3)O3 Microwave Dielectrics: III. Effect of the Muffling Environment

The effect of different muffling environments on the structure and dielectric losses of Ba(Zn1/3Nb2/3)O3 (BZN) microwave ceramics was investigated. The microwave dielectric losses of stoichiometric BZN pellets heated in ZnO‐rich environments were severely degraded (e.g. Q×f∼15 000 in ZnO powder) compared with samples muffled in their own powder (Q×f∼80 000). Structure analyses and gravimetric measurements confirmed that the ceramics muffled in ZnO powder or vapor absorb excess ZnO to form non‐stoichiometric solid solutions with reduced cation order and Q. By using starting compositions in the (1−x)BZN−(x)BaNb4/5O3 binary (x=0.04), the stoichiometry can be tailored to ensure that after the uptake of ZnO, the ceramics remain well ordered and are located in a high Q region of the system. For example, ZnO‐vapor‐protected (0.96)BZN−(0.04)BaNb4/5O3 reached a very high Q×f (∼1 05 000) after sintering at 1400°C for 5 h.

Chemical Substitution in Ba(RE1/2Nb1/2)O3 (RE = La, Nd, Sm, Gd, Tb, and Y) Microwave Ceramics and Its Influence on the Crystal Structure and Phonon Modes

Raman spectroscopy was employed to evaluate the crystal structure and phonon modes of chemically substituted Ba(RE1/2Nb1/2)O3 microwave ceramics (RE = La, Nd, Sm, Gd, Tb, and Y). It was verified that these materials could be divided into tetragonal (ceramics with RE = Y, Tb, and Gd) and orthorhombic (RE = Sm, Nd, and La) structures. Lorentzian lines were used to fit the spectra, which presented 9 bands for the first group and 23 bands for the second group of ceramics. The position and width of the phonon modes were determined, and were correlated to the ionic radii and tolerance factors for the different atoms substituted in the B‘-site. It is believed that simple rotational distortions of the oxygen octahedra led to the occurrence of structures other than cubic, which is very difficult to detect by X-ray diffraction or even spectroscopic techniques.