Structures and microwave dielectric characteristics of compounds in vicinity of CaNdAlO 4 in CaO–Nd 2 O 3 –Al 2 O 3 ternary system

Abstract

Single phase ceramics in the vicinity of CaNdAlO₄ in CaO–Nd₂O₃–Al₂O₃ ternary system, such as ternary oxide compound CaNdAl₃O₇ and binary oxide compounds NdAlO₃, CaAl₂O₄, Ca₃Al₂O₆ and Ca₁₂Al₁₄O₃₃, were prepared by the standard solid state reaction route. The phases and structure of the ceramics were analysed through X-ray diffraction and scanning electron microscopy. The microwave dielectric characteristics of the ceramics were studied using a network analyser. High Qf values were obtained in CaNdAlO₄, CaNdAl₃O₇, NdAlO₃ and CaAl₂O₄, while the Qf values in Ca₃Al₂O₆ and Ca₁₂Al₁₄O₃₃ were much lower. The best microwave dielectric characteristics (ϵ_r = 8·9, Qf = 90 800 GHz at ∼9·40 GHz and τ_f≈−55·2 MK⁻¹) were achieved for CaAl₂O₄ ceramics sintered at 1425°C in air for 3 h. It could be expected as a promising new candidate for microwave dielectric ceramics. Moreover, the present results showed the direction for modification of CaNdAlO₄ microwave dielectric characteristics through composition tailoring.