Microwave dielectric properties of A₂P₂O₇ (A = Ca, Sr, Ba; Mg, Zn, Mn)

Microwave dielectric properties of A₂P₂O₇ (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 A₂P ₂O₇ ceramics could be sintered at relatively lower temperature below 1150°C, although the thortveitite type series, Mn ₂P₂O₇, α-Mg₂P ₂O₇ and α-Zn₂P₂O₇ with smaller ionic radii of A cations were hard to sinter to full density. The dielectric constant of A₂P₂O₇ is lower than 10. The Q × f value increased according to the sequence of δ-Ba ₂P₂O₇, α-Sr₂P ₂O₇ and β-Ca₂P₂O₇ in dichromatic type series, and the sequence of Mn₂P ₂O₇, α-Mg₂P₂O₇ and α-Zn₂P₂O₇ in thortveitite type series, respectively. The temperature coefficient of resonant frequency τ _f for all samples exhibits negative value. Larger τ_f for α-Zn₂P₂O₇, α-Mg ₂P₂O₇ and δ-Ba₂P ₂O₇ is mainly due to their reversible phase transformations. The microwave dielectric properties were discussed from the point view of bond valence.