Tham khảo tài liệu 'ferroelectrics material aspects part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 60 Ferroelectrics - Material Aspects Effect of tin doping BTS films The evolution of the capacitance as a function of an electrical field E is given figure for two BTS thin films annealed at 750 C during 1 hour and at 950 C during 15 minutes. The DC electric field variation was in the range -225 kV cm 225 kV cm and the measurement frequency was 10 kHz. The butterfly shape of the curves attests to the ferroelectric behaviour of the two films. The tunability for the annealing temperature of 750 C@1 h is about 40 and for an annealing 950 C@15 min it is 76 under a bias of 225 kV cm. From figure it can be seen that for this field the tunability is close to its saturation value. To the best of our knowledge the value of 76 is the highest reported for a doped BaTiO3 thin film deposited by sol-gel Mascot et al 2011 . Indeed for example 45 have been obtained but with a very high electric field of 400 kV cm for a film Song et al 2006 . Our tunability of 76 corresponds to a variation by a factor 4 of the capacitance and by consequence of the dielectric permittivity. Such a variation can be well compared to the one of a varactor diode and is very interesting as stated before for the realization of tunable devices in radiofrequencies and microwaves. Fig. 13. Evolution at 10kHz of the capacitance as a function of a DC field for BTS films annealed at 750 C and 950 C a tunability evolution of the BTS film annealed at 950 C. Influence of the substrate We study here the ferroelectric properties of BST films deposited on a low cost stainless steel substrate compared with the ones on higher cost Si Pt substrates. C E and hysteresis cycle We consider the BST films deposited on stainless steel substrates on which we have made dielectric measurements . In figure we present the evolution at 1 kHz of the reduced values of the capacitance as a function of a DC field for BST films deposited in the same conditions either on Si Pt or .
