Variation of electrical properties with structural vacancies in ferroelectric niobates (Sr0.53Ba0.47)2.5−0.5Na Nb5O15 ceramics

Abstract

(Sr0.53Ba0.47)2.5-0.5xNaxNb5O15 ceramics (SBNN, 0.0 ≤ x ≤ 2.5) were prepared by the conventional solid-state reaction method. The Na + concentration varied from 0.0 to 2.5 so that the tetragonal tungsten bronze (TTB) crystal structure was designed to transform from 'unfilled' to 'filled' and then to 'stuffed' type. Apart from the change in the structural type, the effects of Na + concentration on the phase structure as well as microstructure, ferroelectric and dielectric properties were also investigated. X-ray diffraction analysis revealed that the crystallized SBNN ceramics with x ≤ 1.0 had the tetragonal tungsten bronze structure with space group of P4bm. With further increasing x above 1.0, the broad asymmetrical diffraction peaks near 32 o associated with EDX analyses indicated the existence of some amount of secondary NaNbO3based phase due to the introduction of excessive Na +. It was also found that Na + concentration had a significant influence on the electrical properties of SBNN ceramics. Introducing Na + in A-sites to decrease the structural vacancies and increase the distortion degree of NbO6 polar unit was beneficial for the electric properties, while excessive Na + content would deteriorate the electric properties owing to the presence of secondary NaNbO3-based phase.

Electrical and transparent properties induced by structural modulation in (Sr0.925Ca0.075)2.5–0.5Na Nb5O15 ceramics

“…At x = 0.4, the broad peak associated with the low-temperature dielectric anomaly in the 'unfilled' SCNN ceramics showed obvious relaxor behavior: the position of maximum relative permittivity shifted toward higher temperatures as the frequency increases. The relaxor behavior of the low-temperature dielectric anomaly is similar to that observed in (Sr 0.53 Ba 0.47 ) 2.5−0.5x Na x Nb 5 O 15 and Sr 2 NaNb 5 O 15 ceramics[20,21]. In those materials, the relaxor behavior can be attributed to the smeared-out phasetransition state, combined with subtle structure effects[20,21].…”

“…Correlations among the composition, structure and properties can be studied by modulating the alkali metal ion content in the A-sites of the TB (A1) 2 (A2) 4 Nb 10 O 30 composition to tune the structure (i.e., changing the structure from 'unfilled' to 'filled' type). Previously, we have formed the (Sr 0.53 Ba 0.47 ) 2.5−0.5x Na x Nb 5 O 15 (0.0 ≤ x ≤ 1.0) compounds by introducing the alkali metal Na + into the 'unfilled' Sr 0.53 Ba 0.47 Nb 2 O 6 ceramics [20]. It was found that the low-temperature dielectric anomalies were not observed in 'unfilled' Sr 0.53 Ba 0.47 Nb 2 O 6 ceramics.…”

Enhanced electrical properties and strong red light‐emitting in Eu3+‐doped Sr1.90Ca0.15Na0.9Nb5O15 ceramics

“…The relative permittivity obtained at T s is e s . Rather than the dielectric anomaly corresponding to the smeared-out phasetransition state combined with subtle structure effects observed in (Sr 0.53 Ba 0.47 ) 2.5À0.5x Na x Nb 5 O 15 and Sr 2 NaNb 5 O 15 ceramics, 12,24 this intense low-temperature dielectric anomaly obtained in SCNN:xEu 3+ ceramics is considered as the ferroelastic phase transition related to the orthorhombic (2mm)-tetragonal (4mm) phase. 23,25 With increasing x, the frequency dispersion becomes stronger and the ceramics show obvious relaxor type behavior with a distinct shift of e s to higher temperatures as the frequency increases.…”

“…The complete occupation of all above A1, A2, and C sites corresponds to the 'stuffed' TB structure; C site is generally vacant, then the occupation of 6 A sites refers to the 'filled' TB structure; the occupation with only 5 out of 6 A sites refers to the 'unfilled' structure. 5,8,12 In the past decades, luminescent-ferroelectic materials have aroused considerable attention as that they can be developed for future multifunctional optoelectronic devices within a single material. [5][6][7][8][9][10][11] In addition, niobate materials with the 'filled' TB structure usually exhibit much better dielectric and ferroelectric properties compared to those with the 'unfilled' TB structure.…”

“…[5][6][7][8][9][10][11] In addition, niobate materials with the 'filled' TB structure usually exhibit much better dielectric and ferroelectric properties compared to those with the 'unfilled' TB structure. 5,8,12 In the past decades, luminescent-ferroelectic materials have aroused considerable attention as that they can be developed for future multifunctional optoelectronic devices within a single material. 13,14 Luminescent-ferroelectric performs can be obtained in ferroelectric host materials doped with activator ions.…”