Abstract
(Sr1 − 3x/2Lax)2TiO4 ceramics (0 ≤ x ≤ 0.02) with the tetragonal Ruddlesden-Popper structure (I4/mmm) were synthesized through the conventional solid-state methods. The phase composition, chemical structure and the microwave dielectric properties of the (Sr1 − 3x/2Lax)2TiO4 ceramics were investigaed. The single phase was obtained for x < 0.02. The substitution of La3+ for Sr2+ could decrease the ionic polarizability and the cell volume, Which slightly decrease the dielectric constant (er), the quality factor (Q × f) were closely related to the packing fraction, while the temperature coefficient of resonant frequency (τf) is correlated to the tolerance factor. Which attributed to the increase of the Q × f value and the decrease of the τf value. The optimum microwave dielectric properties for (Sr1-3x/2Lax)2TiO4 were obtained in x = 0.015 (er = 34.07, Q × f = 86,450 GHz and τf = + 91.8 ppm/oC). Besides, in order to further decrease the τf value, the Sr1.955La0.03Ti1 − yCeyO4 ceramics were also synthesized through the conventional solid-state methods. A near-zero τf value was achieved in y = 0.7 (er = 20.18, Q × f = 87651 GHz and τf = − 0.2 ppm/°C).
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