SrLn ₂ Al ₂ O ₇ (Ln = La, Nd, Sm) Microwave Dielectric Ceramic New Materials

SrLn 2 Al 2 O 7 (Ln = La, Nd, Sm) ceramics were proposed and investigated as new candidates for ultra‐low loss microwave dielectric materials. These ceramics indicated the Ruddlesden–Popper structure of general formula A n +1 B n O 3 n +1 with n = 2, which was composed by n perovskite layers alternating with one rock‐salt layer. Very high Qf value combined with a dielectric constant around 20 was obtained in the present ceramics, where the near‐zero temperature coefficient of resonant frequency varied from negative to positive with changing Ln from La to Sm. The best combination of microwave dielectric characteristics was obtained as the following: ε r = 18.2, Qf = 71,680 GH z, and τ f = −22.1 ppm/°C for SrLa 2 Al 2 O 7 ; ε r = 20.5, Qf = 65,500 GH z, and τ f = −4.3 ppm/°C for SrNd 2 Al 2 O 7 ; and ε r = 21.6, Qf = 64,680 GH z, and τ f = +4.0 ppm/°C for SrSm 2 Al 2 O 7 .

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