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Nouveaux matériaux perovskites ferroélectriques : céramiques et couches minces issues de la solution solide (Sr₂Ta₂O₇)₁₀₀₋ₓ(La₂Ti₂O₇)ₓ

Abstract : This research focuses on the study of a new material resulting from the combination of two ferroelectric perovskite oxides Sr2Ta2O7 and La2Ti2O7; the resulting solid solution is formulating according to (Sr2Ta2O7)100 x(La2Ti2O7)x (STLTO). Our study includes the synthesis of powders, the realization of ceramics, thin film deposition and their structural, morphological, elemental, optical, dielectric and ferroelectric characterizations. The medium-term objective for this material is its integration into miniature and reconfigurable microwave devices. For this, high permittivity, variable under electric field, is required in order to achieve a tunability of the material, then a reconfigurability of the antennas, for example. Structural analysis by X-ray diffraction confirmed, by the linear variation of the cell parameters, the formation of the solid solution for the compositions x ∊ [0-5]. The dielectric analyzes carried out at low frequencies (1 - 100 kHz) on STLTO ceramics showed maximum values of permittivity (375) and tunability (55% at 3 kV/cm), associated with weak loss tangents (0,01), for the composition x = 1.65. The measurements at high frequencies (200 MHz – 18 GHz) are in agreement with the results obtained at low frequencies. The deposition of thin film by reactive sputtering, made from a target of composition x = 1.65, produces films similar at Sr2.83Ta5O15 phase, which denotes a loss of strontium. However, at low frequencies, the films have relatively high permittivity (130) for low losses (0.01) with moderate tunability (A= 14.5% at 340 kV/cm at f = 100 kHz). Deposition of oxynitride thin film (Sr,La)(Ta,Ti)O2N, carried out in Ar + N2 reactive atmosphere, leads to coloured samples having high permittivity (up to about 3000), but with equally high losses (up to 2) and without tunability. Moreover, the study of SrTaO2N showed that these compounds are suitable for the decomposition of water under visible light.
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https://tel.archives-ouvertes.fr/tel-01917556
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Submitted on : Friday, November 9, 2018 - 3:03:07 PM
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Florent Marlec. Nouveaux matériaux perovskites ferroélectriques : céramiques et couches minces issues de la solution solide (Sr₂Ta₂O₇)₁₀₀₋ₓ(La₂Ti₂O₇)ₓ. Electronique. Université Rennes 1, 2018. Français. ⟨NNT : 2018REN1S024⟩. ⟨tel-01917556⟩

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