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.
Synthesis and characterization of doped LaCrO3 perovskite prepared by EDTA–citrate complexing method
Abstract The La0.85Sr0.15Cr0.95Ni0.02Co0.02O3 (LSC) interconnect materials for solid oxide fuel cells (SOFCs) were synthesized by EDTA–citrate complexing method. Thermal decomposition behavior of the gel, phase formation and morphology of LSC powders were characterized by thermogravimetry/differential thermal (DSC/TG) analysis, X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. It appeared that lower pH value (pH 4.9) of the precursor solution resulted in a transient liquid phase, SrCrO4, in the calcined LSC powder. The sintering characteristics, electrical conductivity and thermal expansion properties of sintered bars were investigated. La0.85Sr0.15Cr0.95Ni0.02Co0.02O3 prepared in the condition of pH 4.9 showed an electrical conductivity of 15.6 S cm−1 at 800 °C and a thermal expansion coefficient (TEC) of 10.8 × 10−6 K−1 (20–900 °C), which is suitable for use as interconnect materials for SOFCs.