Anomalous Thermal Behavior of CuxMg1-xNb2O6 (x=0,0.4,0.6,1) for LTCC Substrate
LTCC (Low Temperature Co-fired Ceramics) being the most advantageous technology towards the multilayer substrates for various applications, demands an extensive study of its raw materials. In the present work, a series of CuxMg1-xNb2O6 (x=0,0.4,0.6,1) has been prepared using sol-gel synthesis route and sintered at a temperature of 900°C to study its applicability for LTCC technology as the firing temperature is 900°C in this technology. The phase formation has been confirmed using X-ray Diffraction. Thermal properties like thermal conductivity and thermal expansion being very important aspect as the former defines the heat flow to avoid thermal instability in layers and the later provides the dimensional congruency of the dielectric material and the conductors, are studied here over high temperature up to the firing temperature. Although the values are quite satisfactory from substrate requirement point view, results have shown anomaly over temperature. The anomalous thermal behavior has been further analyzed using TGDTA. Keywords—Niobates, LTCC, Thermal conductivity, Thermal expansion, TG-DTA.
Luminescent and structural properties of MgNb2O6 nanocrystals
Abstract This study investigated the synthesis and luminescence properties of MgNb2O6 nanocrystals by citric gel process. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy, and photoluminescence (PL). The PL spectra excited at 270 nm had a broad and strong blue emission band maximum at 450 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO6]7−. The optical absorption spectra of the 800 °C sample exhibited the band-gap energy of 3.6 eV. Furthermore, the microstructure and luminescence spectra of the products were investigated.
Ordering-Induced Microstructures and Microwave Dielectric Properties of the Ba(Mg1/3Nb2/3)O3–BaZrO3 System
The structures of compositions across the Ba(Mg 1/3 Nb 2/3 )-O 3 -BaZrO 3 (BMN-BZ) system have been examined using X-ray diffractometry and transmission electron microscopy, and their dielectric properties have been characterized in the microwave range. Although pure BMN adopts a 1:2 ordered structure, of space group Pm31, additions of 5-15 mol% BZ stabilize a cubic (Fm3m), 1:1 ordered phase with a doubled perovskite repeat. At higher levels of substitution (>25 mol% BZ), the B-site cations are disordered. After normal sintering, the niobates in the 1:1 phase field are comprised of nanometer-sized ordered domains that are dispersed in a disordered matrix. However, by reducing the cooling rate to 10°C/h, a fully ordered microstructure is formed with domain sizes >100 nm in size. The structure of the 1:1 phases has been interpreted using a random-layer model, in which one site is occupied by niobium, and the second is occupied by a random distribution of the remaining cations. The addition of small concentrations of BZ produces a 100% improvement in the dielectric-loss properties of BMN, and a Q.f value of 82000 is obtained for a 5 mol% substitution.