| With the rapid development of IT especially the electronic and microelectronic industry, it has given a higher request to dielectric materials. How to increase the permittivity, decrease the dielectric loss and improve their temperature- and frequency-dependence has been one of important research goals for dielectric materials. This paper has taken Sr Ti O3 ceramics as the research objects and analyzed the changes in structures and dielectric properties by study on nonstoichiometry and doping with different elements, and improved the dielectric properties of Sr Ti O3 ceramics, and achieved the dielectric materials with giant permittivity, low dielectric loss and weak temperature- and frequency-dependence.This paper has investigated effects of nonstoichiometry on the crystal structures, microstructures and dielectric properties of the Sr Ti O3 ceramics by changing the Sr/Ti values. The results showed that when the Sr/Ti values changed from 0.994 to 1.004, no matter the Sr/Ti values were less or more than 1, the grain size decreased. The room-temperature dielectric properties of the nonstoichiometric Sr Ti O3 ceramics were similar with the permittivity of about 300 and the dielectric loss of less than 0.01 measured at 25 °C and 1 k Hz. The dielectric relaxation of the ceramics sintered in air at high temperatures was due to the interfacial effects. Sr Ti O3 ceramics sintered in N2 at 1440 °C showed giant permittivity and low dielectric loss. The permittivity and dielectric loss for the Sr Ti O3 ceramics sintered in N2 at 1440 °C measured at 25 °C and 1 k Hz were 47601 and 0.0058, respectively. The dielectric behaviors of the Sr Ti O3 ceramics sintered in N2 at 1440 °C were due to the [TiVe TieO·--·44+··+] bond, in which the electrons were bound by Ti4+ and ··OV, leading to low dielectric loss.The dielectric properties changed obviously when the Sr0.996 Ti O3 ceramics sintered in N2 at different temperatures. When the Sr0.996 Ti O3 ceramics sintered in N2 at 1400 °C, the permittivity and dielectric loss measured at 25 °C and 1 k Hz were 3639 and 0.09, respectively. However, the permittivity increased to 30722, and the dielectric loss decreased to 0.0042 when the Sr0.996 Ti O3 ceramics sintered in N2 at 1500 °C. The results showed that the increase in the sintering temperature could decrease the interfacial effects and improve the dielectric properties. The permittivity and dielectric loss of the Sr1.004 Ti O3 ceramics sintered in N2 at 1500 °C measured at 25 °C and 1 k Hz were 292 and 0.002, respectively. The dielectric relaxation of the Sr1.004 Ti O3 ceramics sintered in N2 at 1500 °C at high temperatures was due to the interfacial effects.The grain sizes of the Sr Ti Zrx O3 and Sr Cax Ti O3 ceramics decreased with the Zr or Ca content increasing. The permittivity of the Sr Ti Zrx O3 and Sr Cax Ti O3 ceramics sintered in air measured at 25 °C and 1 k Hz was about 300, the dielectric loss were all less than 0.01 and the dielectric relaxation at high temperatures was due to the interfacial effects. The Sr Ti Zrx O3 ceramics sintered in N2 whose dielectric behaviors could be ascribed to the [TiVe TieO·--·44+··+] and [··?-OSrVV ] bonds showed giant permittivity and low dielectric loss, with the permittivity of more than 18000 and the dielectric loss of about 0.003 measured at 25 °C and 1 k Hz. The dielectric behaviors of the Sr Cax Ti O3 ceramics sintered in N2 were similar to that sintered in air, with the permittivity of about 300 and the dielectric loss of less than 0.01 measured at 25 °C and 1 k Hz. The dielectric relaxation at high temperatures was due to the interfacial effects.The unit cell volume of the Sr Ti0.99(Al, Zr, Nb)0.01O3 ceramics increased with the ionic radii of doping ions increasing. When Sr Ti0.99(Al, Zr, Nb)0.01O3 ceramics were sintered in N2, Al3+ ions could stabilize the Ti4+ ions,Nb5+ ions could promote the formation of Ti3+ ions and Zr4+ ions could stabilize some Ti4+ ions. Both Sr Ti0.99Al0.01O3 ceramics sintered in air and N2 and Sr Ti0.99Zr0.01O3 ceramics sintered in air displayed the similar dielectric properties with the permittivity of about 300 and the dielectric loss of less than 0.01 measured at 25 °C and 1 k Hz. The dielectric relaxation of them at high temperatures was due to the interfacial effects. The permittivity and dielectric loss of the Sr Ti0.99Nb0.01O3 ceramics sintered in air measured at 25 °C and 1 k Hz were 4651 and 0.05, respectively. The dielectric behaviors of the Sr Ti0.99Nb0.01O3 ceramics sintered in air were attributed to the ionization of the oxygen vacancies. The permittivity and dielectric loss of the Sr Ti0.99Nb0.01O3 ceramics sintered in N2 measured at 25 °C and 1 k Hz were 23601 and 0.0051, respectively. The dielectric behaviors of the Sr Ti0.99Nb0.01O3 ceramics sintered in N2 could be due to the [ e Tie TV iO·--·44+··+] bond. The permittivity and dielectric loss of the Sr Ti0.99Zr0.01O3 ceramics sintered in N2 measured at 25 °C and 1 k Hz were 9723 and 0.035, respectively. The dielectric behaviors of the Sr Ti0.99Zr0.01O3 ceramics sintered in N2 were due to the interfacial effects.For the Sr0.9775Sm0.015 Ti O3 ceramics, doping with Sm resulted in the decrease of the unit cell volume. The permittivity and dielectric loss of the Sr0.9775Sm0.015 Ti O3 ceramics sintered in air measured at 25 °C and 1 k Hz were 9040 and 0.04, respectively. The dielectric behaviors of the Sr0.9775Sm0.015 Ti O3 ceramics sintered in air were relate to the ionization of oxygen vacancies, while it could be due to the [TiVe TieO·--·44+··+] bond for the Sr0.9775Sm0.015 Ti O3 ceramics sintered in N2, whose permittivity and dielectric loss are 40324 and 0.006, respectively. The dielectric relaxation of the Sr0.9775Sm0.015 Ti O3 ceramics sintered in N2 at high temperatures could be explained by the interfacial effects.The ?25D/ CC at 1 k Hz and 100 k Hz of the N2-STZ10?N2-STN and N2-SST0.015 ceramics are less than 15 %, which are measured at the temperature range from-55 to 125 °C and could meet the requirements of the high permittivity capacitor(X7R). |
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