Structure and microwave dielectric properties of ALn4(MoO4)7 (A = Ba,Sr, Ca,Ln = La,Pr, Nd,and Sm) ceramics

ALn₄(MoO₄)₇ (A = Ba, Sr, Ca, Ln = La, Pr, Nd, Sm) ceramics are prepared by solid state ceramic route and the structural properties have been studied using powder X-ray diffraction and laser Raman spectroscopy. All the ceramics under study are phase pure except BaLn₄(MoO₄)₇ (Ln = Pr, Nd, Sm). Scanning electron micrographs of the sintered ceramics show closely packed microstructure with phase homogeneity. BaLa₄(MoO₄)₇ ceramic has a maximum density of 4.5 g/cm³ at 710°C together with ԑ_r = 11.8, Q_u x f = 39 300 GHz, and τ_f = −68 ppm/^oC. SrLa₄(MoO₄)₇ ceramic exhibited a maximum density of 4.4 g/cm³, ԑ_r = 11.7, Q_u x f = 44 200 GHz, and τ_f = −83 ppm/^°C at 740°C whereas CaLa₄(MoO₄)₇ ceramic possess a maximum density of 4.2 g/cm³, ԑ_r = 11.4, Q_u x f = 30 200 GHz and τ_f = −90 ppm/^oC at 750°C at microwave frequencies. The chemical compatibility of the BaLa₄(MoO₄)₇, SrLa₄(MoO₄)₇ and CaLa₄(MoO₄)₇ ceramics with silver electrode have been studied using powder X-ray diffraction of the co-fired samples and is further examined with energy dispersive X-ray spectroscopy.