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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]

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.