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.
Cation Ordering and Dielectric Characteristics in Barium Zinc Niobate
Barium zinc niobate (Ba(Zn1/3Nb2/3)O3) (BZN) complex perovskite has been reported to have special microwave dielectric properties with close relation of its ordered structure. This study investigated the effect of calcination on the evolution of ordered structure and on quality factor with Raman spectroscopy, X-ray diffractometry, and transmission electron microscopy. The results revealed that single calcination at a lower temperature inhibited the growth of the ordered domain during sintering. In contrast, the 1:2-ordered domain in double-calcined BZN powder grew significantly with a higher sintering temperature and a longer soaking time. It is attributed that double calcination caused a higher degree of 1:2 ordering and better homogeneity. At the same time, the quality factor of the sintered ceramic body was highly promoted when using double-calcined powder. A close relation of the quality factor with the size of ordered domain, the degree of 1:2 ordering, and the relative density of BZN ceramics was presented.
Effect of Structural Changes on the Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Ceramics
The microstructure and microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 (BZN) ceramics have been investigated. BZN has a 1:2 ordered hexagonal structure, and the degree of 1:2 ordering decreased with increasing sintering temperature. Liquid phase was found for the BZN sintered at more than 1350°C, the evaporation of ZnO was responsible for the formation of liquid phase. BaNb6O16 second phase was also found for the specimens sintered at more than 1350°C and the liquid phase is considered to have a composition close to that of BaNb6O16 second phase. The Q-value of BZN was increased with increasing sintering temperature and BZN sintered at 1400°C for 6 h has the maximum Q-value. Since the 1:2 ordering decreased with the sintering temperature, the enhancement of Q-value is not related to the 1:2 ordering. The increase of the average grain size could be responsible for the increase of the Q-value, and the relative density also influenced the Q-value. BZN ceramics were sintered for various times at 1400°C and 1300°C and the variation of Q-value was explained in terms of the grain size and the relative density.