Correlation between crystal structure and microwave dielectric properties of CaRE4Si3O13 (RE = La, Nd, Sm, and Er)
Novel Ca RE 4 Si 3 O 13 (RE = La, Nd, Sm, and Er) microwave dielectric ceramics were prepared using solid-state reaction sintered at 1350–1400 °C for 5 h. CaRE 4 Si 3 O 13 (RE = La, Nd, Sm, and Er) possessed an apatite structure with the P 6 3 /m space group. The lattice parameters a , b and c ; theoretical density and unit cell volumes of CaRE 4 Si 3 O 13 (RE = La, Nd, Sm, and Er) gradually decreased when RE changed from La to Er, and a pure phase was formed at all compositions. The ε r , Q × f , and τ f values of the CaRE 4 Si 3 O 13 (RE = La, Nd, Sm, and Er) ceramics were related to the total ionic polarizability, packing fraction, and polyhedral distortion of RE/Ca(2)O 7 , respectively. The optimal microwave dielectric properties of the CaRE 4 Si 3 O 13 ceramics ( ε r = 13.37, Q × f = 18,600 GHz, and τ f = − 17.8 ppm/°C) were obtained at RE = Er.
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