Microwave Dielectric Properties of A₂P₂O₇ (A = Ca, Sr, Ba; Mg, Zn, Mn)

Abstract

Microwave dielectric properties of A 2 P 2 O 7 (A = Ca, Sr, Ba, Mn, Mg, Ba) ceramic materials were investigated by a network analyzer at the frequency of 10 GHz. It was found that A 2 P 2 O 7 ceramics could be sintered at relatively lower temperature below 1150°C, although the thortveitite type series, Mn 2 P 2 O 7 , α-Mg 2 P 2 O 7 and α-Zn 2 P 2 O 7 with smaller ionic radii of A cations were hard to sinter to full density. The dielectric constant of A 2 P 2 O 7 is lower than 10. The Q × f value increased according to the sequence of δ-Ba 2 P 2 O 7 , α-Sr 2 P 2 O 7 and β-Ca 2 P 2 O 7 in dichromatic type series, and the sequence of Mn 2 P 2 O 7 , α-Mg 2 P 2 O 7 and α-Zn 2 P 2 O 7 in thortveitite type series, respectively. The temperature coefficient of resonant frequency τ f for all samples exhibits negative value. Larger τ f for α-Zn 2 P 2 O 7 , α-Mg 2 P 2 O 7 and δ-Ba 2 P 2 O 7 is mainly due to their reversible phase transformations. The microwave dielectric properties were discussed from the point view of bond valence.