Processing and Characterization of BaTi 4 O 9

BaTi 4 O 9 powder prepared by calcining BaCO 3 and TiO 2 powders was sintered to over 97% of theoretical density. Less than 5% Ba 2 Ti 9 O 20 occurred as a second phase in “pure” BaTi 4 O 9 , and Al 2 O 3 impurities from processing formed isolated hollandite (∼BaAl 2 Ti 6 O 16 ) grains, which were identified by fringes in bright‐field TEM images. For pure BaTi 4 O 9 at 1 MHz, a dielectric loss (tan δ) of 5 × 10 −4 and dielectric constant of 39 were recorded. Hollandite impurities were found to increase tan δ by 2 orders of magnitude, whereas firing in oxygen decreased tan δ by an order of magnitude.