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Enhancing Properties in Microwave Ceramics Using a Designer Sintering Aid
Author(s) -
Nicholls Simon J.,
Reaney Ian M.,
Leisten Oliver P.
Publication year - 2015
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.13788
Subject(s) - sintering , materials science , ceramic , dielectric , ionic bonding , permittivity , valence (chemistry) , temperature coefficient , microwave , analytical chemistry (journal) , relative permittivity , perovskite (structure) , chemical engineering , mineralogy , ion , composite material , chemistry , optoelectronics , organic chemistry , physics , quantum mechanics , engineering
It has recently been shown that 0.2CaTiO 3 –0.8(Li 0.5 Nd 0.5 )TiO 3 ( CTLNT ) with the addition of 4 wt% Bi 4 B 2 O 9 ( BBO ) as a liquid‐phase sintering aid gives rise to exceptional microwave ( MW ) dielectric properties, (relative permittivity, ε r = 125, quality factor, Qf 0 and temperature coefficient of the resonant frequency, τ f = 4 ppm/°C) at reduced sintering temperatures (1200°C). In this study, X‐ray diffraction and scanning and transmission electron microscopy have been used to elucidate the mechanism by which MW dielectric properties are optimized. It is demonstrated that highly polarizable Bi 3+ ions enter the perovskite lattice thereby increasing ε r . The concomitant ex‐solution of TiO 2 as BBO concentration increases implies that ionic compensation occurs through the formation of V Ti ″ ″in the perovskite lattice and infers that Bi 3+ substitutes on the A‐site for lower valence ionic species according to the equation: 4 A A x + Ti Ti x ⇒ 4 Bi A · + V Ti ″ ″. The residual boron rich material acts as a sintering aid with strongly −ve τ f that compensates for the +ve τ f of the perovskite matrix. This mechanism points to a new way of utilizing designer sintering aids in the development of microwave ceramics.