Ultra‐low Sintering Temperature Microwave Dielectric Ceramics Based on Na₂O‐MoO₃ Binary System

Abstract

The compounds in Na2O‐MoO3 system were prepared by the solid‐state reaction route. The phase composition, crystal structures, microstructures, and microwave dielectric properties of the compounds have been investigated. This series of compounds can be sintered well at ultra‐low temperatures of 505°C–660°C. The sintered samples exhibit good microwave dielectric properties, with the relative permittivities (εr) of 4.1–12.9, the Q × f values of 19900–62400 GHz, and the τf values of −115 ppm/°C to −57 ppm/°C. Among the eight compounds in this binary system, three kinds of single‐phase ceramics, namely Na2MoO4, Na2Mo2O7 and Na6Mo11O36 were formed. Furthermore, the relationship between the structure and the microwave dielectric properties in this system has been discussed. The average NaI‐O and MoVI‐O bond valences have an influence on the sintering temperatures in Na2O‐MoO3 system. The large valence deviations of Na and Mo lead to a large temperature coefficient of resonant frequency. The X‐ray diffraction and backscattered electron image results show that Na2MoO4 doesn't react with Ag and Al at 660°C. Also, Na2Mo2O7 has a chemical compatibility with Al at 575°C.

Cold‐Sintered C0G Multilayer Ceramic Capacitors

“…Image contrast shows the microstructures to encompass two chemically distinct and discrete phases with EDS attributing the dark and light contrast regions to NMO and BLVMO, respectively, in agreement with the XRD and Raman results (Figure a,b). The grain size of NMO (5–10 µm) is much larger than that of BLVMO (1–2 µm), consistent with previous reports . Figure c shows an ≈10 µm silver electrode layer, which has a sharp interface with the ceramic grains, supporting good chemical compatibility between grains of the composite and the Ag‐electrode.…”

“…Nevertheless, in many of these LTCC/ULTCC systems it is not always possible to prevent the reaction between the ceramic and electrodes. These reactions are accompanied by either the formation of parasitic phases and/or modification of the electrical properties due to interdiffusion which impairs the functionality of the device. Recently, CSCC has emerged as a new processing route to overcome some of the electrode compatibility issues faced by LTCC/ULTCC systems.…”

“…In this work, (Bi 0.95 Li 0.05 )(V 0.9 Mo 0.1 )O 4 (BLVMO) and Na 2 Mo 2 O 7 (NMO) ceramics with positive and negative TCF of ≈ + 81 and −99 ppm °C −1 , respectively, were selected as end‐members to fabricate novel temperature stable BLVMO‐NMO composites . Temperature stable (<10 ppm °C −1 ) composites with low dielectric loss (tan δ ≈ 0.001) and ε r = 40 were attained which were subsequently used to fabricate MLCCs at 150 °C.…”

“…BLVMO has a tetragonal scheelite structure, with no evidence of splitting of main diffraction peaks. NMO has an orthorhombic structure with symmetry described by the space group Cmca (PDF 01‐073‐1797, a = 7.164 Å, b = 11.837 Å, c = 14.713 Å, Z = 8) . All reflections in the XRD data for BLVMO‐NMO ceramic composites can be ascribed to BLVMO and NMO and there is no apparent shift in peak position, indicating no interaction between these two end members.…”

Temperature Stable Cold Sintered (Bi0.95Li0.05)(V0.9Mo0.1)O4-Na2Mo2O7 Microwave Dielectric Composites

“…In the present work, (Bi 0.95 Li 0.05 )(V 0.9 Mo 0.1 )O 4 (BLVMO, ε r = 76, TCF = +81 ppm/°C) and Na 2 Mo 2 O 7 (NMO, ε r of 11.6, TCF of −99 ppm/°C) were selected as cold sintering end-members to fabricate a composite series with the anticipation for delivering a medium ε r ( ca. 40–50), zero TCF ceramic suitable for MW applications [25,26,27,28]. The potential use CSP composites in a novel graded radial index (GRIN) dielectric lens is discussed.…”