Effect of H_2O on dielectric properties of berlinite. I. Dielectric constant

The dielectric constants of a series of hydrothermally grown berlinite crystals containing increasing amounts of H2O were determined using a two-terminal method and empirically determined edge corrections with k^(T)_(11) ranging from 4.67 to 4.86 and k^(T)_(33) from 4.54 to 4.76. The extrapolated values for 'dry' berlinite are k^(S)_(11)= k^(S)_(33)=4.55. Infrared studies of these crystals show bands at 4400 and 5200 cm^-1 which are attributed respectively to hydroxyl ions and macroscopic and microscopic inclusions of the 6-7 M HCl/H_(3)PO_4 growth medium. The hydroxyl ions are believed to result from terminal P-OH groups at the surfaces of inclusions or as (4H)_Al or (3H)_Al hydroxyl nests. The OH- groups have a negligible influence on the dielectric constant, whereas the inclusions are responsible for the increase in k^(S)_(11) and k^(T)_(33) to 4.8 over the dry value of 4.55