Microwave dielectric properties of Sr3Ti2O7 ceramics with composite element doping of Nd & Al

Sr 3 Ti 2 O 7 microwave dielectric ceramics with Ruddlesden-Popper (R–P) structure were successfully prepared via a solid-state reaction method, and its phase composition, microstructure and properties were systematically studied in this work. Sr 3 Ti 2 O 7 with doping Nd & Al ceramics presented a single-phase Sr 3 Ti 2 O 7 structure in I4/mmm space group. The refined results of XRD showed that the unit cell parameters gradually decreased with the increase of Nd & Al amount. The dielectric constant ( ε r ) was not only affected by ion polarizability, but also related to the factors such as grain size and density. XPS indicated that Nd & Al co-doping effectively eliminated the effect of charge on performance. Raman spectrum showed that the quality factor ( Q f ) was mainly concerned with the FWHM of 633 cm −1 Raman mode and the grain size. In order to further evaluate the change of the temperature coefficient of the resonance frequency ( τ f ), the thermal expansion coefficient ( α ) was further corrected and taken as 20 ppm/°C in this system. The optimal microwave dielectric properties were obtained for composition Sr 2.94 Nd 0.06 Ti 1.94 Al 0.06 O 7 at 1500 °C: ε r = 52.64， Q f = 29954 GHz， τ f = 232.9 ppm/°C. • Further improvement of microwave dielectric properties of Sr 3 Ti 2 O 7 ceramics by Nd & Al co-doping. • Further analysis of the Raman spectrum of the Sr 3 Ti 2 O 7 system. • The effect of co-doping of Nd & Al on the structure of Sr 3 Ti 2 O 3 is investigated. • The corrected thermal expansion coefficient is more suitable for this system than before.