Reaction During Sintering of Barium Titanate with Lithium Fluoride

Abstract

The reactions occurring during sintering of stoichiometric BaTi03 with small additions of LiF were studied at temperatures between 700" and 900°C. BaTi03 reacts with LiF to form a cubic solid solution and Li2Ti03. During sintering, the cubic solid solution coexists with Li2Ti03 and forms a liquid phase at 7 4 0 ' 5°C . The occurrence of a liquid phase at this temperature results in an enhancement of the sintering process and leads to the development of a highly dense microstructure.INTERING of BaTiO, using LiF as an adseveral years. The primary interest in this area arises from the fact that a small addition of L F allows the formation of a liquid phase significantly below the normal sintering temperature of BaTiO,, causing a substantial reduction of the processing temperature for BaTi03-based electronic ceramics. The beneficial effect of L F additions to the sintering of BaTi03 was first reported by Walker et al., who found that 0.5 to 3.0 wt% LiF aided densification of BaTiO, at a much lower temperature than could be achieved without additives. Amin et al. and Anderson et al. have sintered BaTiO, with minor additions of LiF at temperatures below 900°C using long firing periods and obtained BaTiO, capacitors with improved dielectric properties. In a more comprehensive study, Haussonne et ~1 .~have reported the effect of 1 to 2 wt% L F additions on the sintering characteristics and dielectric properties of BaTiO, with variable Ba/Ti ratio and observed that the densification behavior and dielectric properties of the ceramics depend largely on the presence of a pseudocubic perovskite phase, the formation of which requires an excess of Ba. A significant weight loss due mainly to the volatilization of large amounts of both Li and F was observed during sintering which caused a considerable shift of the Curie temperature of BaTiO,. The densification of LiF-fluxed BaTiO, with variable Ba/Ti ratio has also been studied by Tolino and B l~m ,~ who pointed out that the initial Ba/Ti ratio and LiF addition are independently important in determining the densification of BaTiO,. In a recent publication, Desgardin et al. have reported the use of BaLiF3 as a sintering aid which was found to provide a better control of the overall s ' ditive has received much attention for CONTRIBUTING EDITOR-R. M. SPRIGGS

Effect of magnesium niobate precursors on phase formation, microstructure and dielectric properties of perovskite lead magnesium niobate ceramics

“…3. In general, typical PMN microstructure consisting of highly dense grain-packing and round microstructural is observed in both samples and in good agreement with previous works [26,27]. Moreover, the grain sizes are in the range of 2-12 m and 0.8-2.3 m for columbite-and corundumroute PMN ceramics, respectively.…”

“…Micrographs of fracture surface ( Fig. 3 (b) and (d)) show highly dense microstructures consisting of equiaxed grains in agreement with other researchers [26,27,34]. The PMN ceramics also have an intergranular fracture mechanism, indicating that the grain boundaries are mechanically weaker than the grains [35].…”

Niobium-93 MQMAS NMR Spectroscopic Study of Alkali and Lead Niobates

“…magnesium niobate (PMN perovskite), a relaxor ferroelectric, and PMN pyrochlore [78]. Two resonances are easily resolved in the 93 (18.9 and 20.6 MHz) suggests that in these cases the intensities in the 93 Nb 3QMAS spectra are likely quantitatively representative of the relative populations of the corresponding sites.…”

Physical and dielectric properties of BaTiO3–fluoride–glass systems for nitrogen-fireable embedded capacitors

“…There have been numerous reports concerning the utilization of fluoride additives in improving BaTiO 3 -based dielectrics. Most of these reports have been focusing primarily on the effects of fluorides on dielectric or ferroelectric properties of BaTiO 3 sintered at temperatures higher than 1100°C in air atmosphere [8][9][10][11][12]. There have been no systematic reports dealing with the effects of individual fluoride additive, particularly intended for firing at low temperatures in inert atmosphere.…”