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Recent advances in perovskite ferroelectrics have fostered a host of exciting sensors and actuators. Defect engineering provides critical control of the performance of ferroelectric materials, especially lead‐free ones. However, it remains a challenge to quantitatively study the concentration of defects due to the complexity of measurement techniques. Here, a feasible approach to analyzing the A‐site defect and electron in alkali metal niobate is demonstrated. The theoretical relationships among defect concentration, conductivity, and oxygen partial pressure can be established based on the defect chemistry equilibria. The type and concentration of defects are reflected through the conductivity variation with oxygen partial pressure. As a result, the variation of defect concentration gives rise to defect‐driven interfacial polarization, which further leads to distinct properties of the ceramics. e.g. abnormal dielectric behavior. Furthermore, this study also suggests a strategy to manipulate defects and charges in perovskite oxides for performance optimization. [ABSTRACT FROM AUTHOR]

We have investigated the structural and magnetic properties of a novel type of hexaferrite with composition of [Ba.sub.3][M.sub.2][Fe.sub.23[O.sub.41] (where M = Co and Mn) (Z hexaferrite) with tunable permeability. The material is promising for very high frequency (VHF) control when used in a voltage-controlled oscillator (VCO) as a tunable inductor. We substituted Mn for Co in the composition [Ba.sub.3][Co.sub.2-x][Mn.sub.x][Fe.sub.23][O.sub.41] from x = 0.0 to 1.2 to improve the inductance tunability and quality factor of the inductor material. Mn substitution had significant influence on the grain size of the sintered hexaferrites, and the coercivity was greatly reduced. The initial permeability and quality factor increased with increasing substitution of Mn for Co until x reached 0.5, an effect attributed to the decrease of the magnetocrystalline anisotropy constant of the hexaferrite and increase of average grain size. The tunability of the samples also increased with increasing Mn substitution, reaching a maximum at x = 0.5, and then decreased with further substitution. This behavior is similar to that of the initial permeability and coercivity, and can be explained by the same mechanism. Index Terms--Magnetic properties, nonlinear magnetic properties, tunability, Z-type hexaferrite.

Abstract: K0.5(Nd1−xBix)0.5MoO4 (0.2 ≤ x ≤ 0.7) ceramics were prepared via the solid‐state reaction method. All ceramics densified below 720°C with a uniform microstructure. As x increased from 0.2 to 0.7, relative permittivity (ɛr) increased from 13.6 to 26.2 commensurate with an increase in temperature coefficient of resonant frequency (TCF) from – 31 ppm/°C to + 60 ppm/°C and a decrease in Qf value (Q = quality factor; f = resonant frequency) from 23 400 to 8620 GHz. Optimum TCF was obtained for x = 0.3 (−15 ppm/°C) and 0.4 (+4 ppm/°C) sintered at 660 and 620°C with ɛr ~15.4, Qf ~19 650 GHz, and ɛr ~17.3, Qf ~13 050 GHz, respectively. Ceramics in this novel solid solution are a candidate for ultra low temperature co‐fired ceramic (ULTCC) technology. [ABSTRACT FROM AUTHOR]

A series of (1 −x)BiVO4–xLaNbO4 (0.0 ≤x≤ 1.0) ceramics were prepared via a solid state reaction method. A scheelite-structured solid solution was formed for x≤ 0.5 but for x ＞ 0.5, tetragonal scheelite, monoclinic LaNbO4-type and La1/3NbO3 phases co-existed. As x increased from 0 to 0.1, the room temperature crystal structure gradually changed from monoclinic to tetragonal scheelite, associated with a decrease in the ferroelastic phase transition temperature from 255 °C (BiVO4) to room temperature or even below. High sintering temperatures were also found to accelerate this phase transition for compositions with x≤ 0.08. Temperature independent high quality factor Qf ＞10 000 GHz in a wide temperature range 25–140 °C and high microwave permittivity εr∼76.3 ± 0.5 was obtained for the x = 0.06 ceramic sintered at 800 °C. However, small changes in composition resulted in a change in the sign and magnitude of the temperature coefficient of resonant frequency (TCF) due to the proximity of the ferroelastic transition to room temperature. If TCF can be controlled and tuned through zero, then (1 −x)BiVO4–xLaNbO4 (0.0 ≤x≤ 1.0) is a strong candidate for microwave device applications. [ABSTRACT FROM AUTHOR]

In the present work, a series of scheelite-related ( Li0.5 Ln0.5) MoO4 ( Ln = Nd, Er, Gd, Y, Yb, Sm, and Ce) ceramics were prepared by using the solid-state reaction method. Except for the ( Li0.5 Yb0.5) MoO4, the other compositions were found to have a scheelite structure. Among all the compositions, the ( Li0.5 Sm0.5) MoO4, ( Li0.5 Nd0.5) MoO4, and ( Li0.5 Ce0.5) MoO4 ceramics were found to possess low sintering temperatures below melting point of aluminum (660°C) and be chemically compatible with Al. The relation between microwave dielectric properties and structure was analyzed by using the Shannon additive rule and bond-valence theory. This series of microwave dielectric ceramics might be candidate for low temperature co-fired ceramics technology. [ABSTRACT FROM AUTHOR]

Ag2 MoO4 ceramic was prepared by using the solid-state reaction method, which could be sintered at 450°C for 2 h, having a relative permittivity of 8.08, a Qf value of 17 000 GHz, and a temperature coefficient of resonance frequency about −133 ppm/°C. Ag2 MoO4 ceramic was chemically compatible with silver but reacted seriously with aluminum to form ( Ag0.5 Al0.5) MoO4 during the sintering. The fitting of infrared spectra and the Shannon's additive rule were employed to study intrinsic dielectric behaviors of the ceramics at microwave region. Ionic displacive polarization and the electronic polarization contributed almost equally to the dielectric permittivity of the ceramic at microwave region. The Ag2 MoO4 ceramics could be a good candidate for ultra-low temperature co-fired microwave devices. [ABSTRACT FROM AUTHOR]

In the present work, ( Bi1− x Fe x) VO4 ( x ≤ 0.40) ceramics were prepared using the solid-state reaction method. All the ceramics could be well densified at sintering temperatures below 800°C. X-ray diffraction ( XRD) results showed that monoclinic solid solution was formed within x ≤ 0.08. When x ≥ 0.10, both monoclinic scheelite and FeVO4 phases were detected. The ( Bi0.92 Fe0.08) VO4 sample sintered at 720°C for 2 h had a permittivity of 57.5 and a Qf value of 15 000 GHz. The IR reflectivity was fitted to study the intrinsic dielectric properties, showing that the majority of the dielectric contribution for this system at microwave region was attributed to the absorptions of structural phonon oscillation in infrared region. [ABSTRACT FROM AUTHOR]

The effects of thermal annealing treatments on fatigue recovery of lead zirconate titanate ferroelectric thin films were investigated. The PZT thin films were prepared on Pt/TiOx/SiO2/Si electrode stacks using a chemical solution deposition method. It was found that the recovery extent of the remnant polarization, coercive electric field and relative dielectric constant depended on the annealing temperature. It was also found that the fatigue endurance of the annealed samples decreased monotonically with increasing fatigue/annealing periods with an annealing temperature of 700°C. Based on the results, a separate passive regions hypothesis for ferroelectric fatigue was proposed, which could explain the results reasonably. [ABSTRACT FROM AUTHOR]

Electrical properties of ferroelectric thin films depend on the quality of not only the ferroelectric thin layer but also the ferroelectric/electrode interfaces. In the present study, attempts were made to minimize the Pb depletion at the bottom electrode/ferroelectric interface in lead zirconate titanate ferroelectric thin films by adding a PbO interfacial layer using a chemical solution deposition method. The crystallographic structure of the PZT thin films with and without PbO layer were examined by X-ray diffraction. The microstructure of the thin film samples was characterized using optical microscope and atomic force microscope. [ABSTRACT FROM AUTHOR]

This letter reports a novel concept of vertical stacked-spiral RF inductor with integrated nano-powder-magnetic-core in standard CMOS. A proof-of-concept design in a foundry 0.18 \mum 6-metal CMOS using a new post-CMOS backend process (CMOS+) is depicted. Measurement shows significant improvement in inductance (L) of 35% and quality factor (Q) of 41% up to multi-GHz in prototype. An L-density of 420 nH/mm^2 at 1.2 GHz is achieved. Limiting factors for the relatively low Q factor in the prototypes and improvement method are discussed. [ABSTRACT FROM PUBLISHER]

Ni/hexagonal-ferrite (Co2Z or Zn2Y barium ferrites)/polymer composites were prepared for electromagnetic interference (EMI) shielding materials. In comparison with the hexagonal-ferrite/polymer or Ni/polymer composites, such three-phase composites exhibit excellent microwave absorption properties in the X-band frequency range, strongly depending on the combination of these three phases. For the Ni/Co2Z/polymer composites with volume fraction ratio of Ni/ferrite equal to 0.70/0.30, the EMI shielding effectiveness (SE) of the composites with a thickness of 2 mm can be as high as ∼67 dB. The high EMI SE of the composites and much larger contribution to total EMI SE from absorption than from reflection suggest that these composites would be very promising for applications as thinner and lighter EMI absorption materials. [ABSTRACT FROM AUTHOR]

The effects of CuO, Bi2O3 and V2O5 additions on the microstructure and the microwave dielectric properties of ZnNb2O6 ceramics were investigated systematically. The sintering temperature of ZnNb2O6 ceramics with CuO, Bi2O3 and V2O5 (CuBiV) additions can be effectively reduced from 1150 to 890 °C. The presence of CuBiVZn-rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The 1.5 wt.% CuBiV-doped ZnNb2O6 ceramics sintered at 890 °C have the optimum microwave dielectric properties. [Copyright &y& Elsevier]

The electromagnetic and dielectric properties of Mn substituted Ba3Co2Fe23−12xMn12xO41 (Z-type) hexaferrites where 0≤x<0.1 were investigated in this study. The ferrite samples behaved as a semiconductor, and DC resistivity as well as activation energy for electronic conduction increased as the amount of Mn substituted for Fe increased, reaching maximum around x=0.02, and then decreased with further substitution. The behavior of dielectric constant was in an opposite manner to that of the activation energy and DC resistivity. Conduction is explained on hopping of electrons between Fe2+ and Fe3+. It was inferred that the initial permeability was sensitively controlled by the substitution of Mn because of magnetostriction compensation. Low-temperature sintered Co2Z hexaferrite with the substitution of Mn for Fe with low dielectric constant and high initial permeability is suitable for very high frequency (VHF; 300–800 MHz) multilayer chip inductors (MLCI) use. [Copyright &y& Elsevier]

Abstract: ZnTa2O6 microwave dielectric ceramics have been prepared using ZnTa2O6 nano-powders synthesized by sol–gel processing in this study. The crystal structure and microstructure of the ZnTa2O6 powders and ceramics were characterized by XRD and SEM techniques. ZnTa2O6 ceramics can be densified at a lower sintering temperature of 1200°C. Microwave dielectric properties show that both of Q × f and ɛ r values are lower than those of ceramics prepared by solid state route, and the τ f values do not show different from that of solid state route. ZnTa2O6 ceramics sintered at 1200°C exhibit good microwave dielectric properties: Q × f =50,600GHz, ɛ r =35.12 and τ f =9.69ppm/°C. [Copyright &y& Elsevier]

Recent advances in perovskite ferroelectrics have fostered a host of exciting sensors and actuators. Defect engineering provides critical control of the performance of ferroelectric materials, especially lead-free ones. However, it remains a challenge to quantitatively study the concentration of defects due to the complexity of measurement techniques. Here, a feasible approach to analyzing the A-site defect and electron in alkali metal niobate is demonstrated. The theoretical relationships among defect concentration, conductivity, and oxygen partial pressure can be established based on the defect chemistry equilibria. The type and concentration of defects are reflected through the conductivity variation with oxygen partial pressure. As a result, the variation of defect concentration gives rise to defect-driven interfacial polarization, which further leads to distinct properties of the ceramics. e.g., abnormal dielectric behavior. Furthermore, this study also suggests a strategy to manipulate defects and charges in perovskite oxides for performance optimization., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

In this work, the (Na 0.5 Bi 0.5 )(Mo 1-x W x )O 4 (x = 0.0, 0.5 and 1.0) ceramics were prepared via solid state reaction method. All the samples can be well densified at sintering temperature about ~720 °C. Dense and homogeneous microstructure with grain size lying between 2~8 μm can be observed from scanning electron microscopy (SEM). Microwave dielectric permittivity of the (Na 0.5 Bi 0.5 )(Mo 0.5 W 0.5 )O 4 ceramic was found to be temperature-independent in a wide range between 25~120 °C with a temperature coefficient of frequency (TCF) ~-6 ppm/°C, a permittivity ~28.9, and Qf values 12,000~14,000 GHz. Crystal structure was refined using Rietveld method and lattice parameters are a = b = 5.281 (5) Å and c = 11.550 (6) Å with a space group I 4 1 /a (88). The (Na 0.5 Bi 0.5 )(Mo 1-x W x )O 4 ceramics might be good candidate for low temperature co-fired ceramics (LTCC) technology.

With growing concern over world environmental problems and increasing legislative restriction on using lead and lead-containing materials, a feasible replacement for lead-based piezoceramics is desperately needed. Herein, we report a large piezoelectric strain (d 33 *) of 470 pm/V and a high Curie temperature (T c ) of 243 °C in (Na 0.5 K 0.5 )NbO 3 -(Bi 0.5 Li 0.5 )TiO 3 -BaZrO 3 lead-free ceramics by doping MnO 2 . Moreover, excellent temperature stability is also observed from room temperature to 170 °C (430 pm/V at 100 °C and 370 pm/V at 170 °C). Thermally stimulated depolarization currents (TSDC) analysis reveals the reduced defects and improved ferroelectricity in MnO 2 -doped piezoceramics from a macroscopic view. Local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrates the enhanced ferroelectricity and domain mobility from a microscopic view. Distinct grain growth and improvement in phase angle may also account for the enhancement of piezoelectric properties.

In the present work, the microwave dielectric ceramic (Ag0.5Bi0.5)(Mo0.5W0.5)O4 was prepared by using the solid-state reaction method. (Ag0.5Bi0.5)(Mo0.5W0.5)O4 was found to crystallize in the scheelite structure, in which Ag(+) and Bi(3+) occupy the A site randomly with 8-coordination while Mo(6+) and W(6+) occupy the B site with 4-coordination, at a sintering temperature above 500 °C, with lattice parameters a = b = 5.29469(2) Å and c = 11.62114(0) Å, space group I4(1)/a (No. 88), and acceptable Rp = 9.38, Rwp = 11.2, and Rexp = 5.86. High-performance microwave dielectric properties, with permittivity ∼26.3, Qf value ∼10,000 GHz, and temperature coefficient ∼+20 ppm/°C, were obtained in the sample sintered at 580 °C. Its chemical compatibility with aluminum at its sintering temperature was revealed and confirmed by both X-ray and energy dispersive spectrometer analysis. This ceramic could be a good candidate for ultralow-temperature cofired ceramics.