FeTiTaO₆: A Lead‐Free Relaxor Ferroelectric Based on the Rutile Structure

Abstract

Several materials properties of rutile TiO 2 (together with its other polymorphs) have been widely investigated in view of both fundamental and practical interest. It is a wide band gap (E g ¼ 3.05 eV) semiconductor that finds application, among others, as a photocatalyst for splitting water [1] into H 2 and O 2 and remediation of organic pollutants. [2] Among the lesswell-known properties of TiO 2 is its abnormally large static dielectric permittivity that shows strong frequency dependence as well as the associated soft A 2u mode that decreases with decreasing temperature. [3,4] The latter, however, never becomes completely soft, even at 0 K. Accordingly, rutile is classified as an incipient ferroelectric. We prepared M 0 TiTaO 6 (M 0 ¼ Al, Cr, Fe) oxides by conventional solid-state synthesis starting from pure binary oxides. Powder X-ray diffraction (XRD) showed formation of rutile structure for all three M 0 TiTaO 6 compounds. All the reflections in the patterns (Fig. 1) could be indexed to the tetragonal rutile structure. The structural parameters derived from Rietveld refinement of the powder XRD data are given in Table 1. We see that while the c/a ratio remains nearly the same as in the parent rutile TiO 2 , the a and c parameters of M 0 TiTaO 6 show variations that are consistent with the average ionic radii of the metal atoms. We find that the average M-O distances in FeTiTaO 6 are slightly larger than those in rutile, consisting of 4 short and 2 long M-O bonds (elongated MO 6 octahedron); curiously, for M 0 ¼ Al and Cr oxides we find 4 long and 2 short M-O bonds (compressed MO 6 octahedron).We have recorded neutron diffraction (ND) patterns of M 0 ¼ Cr, Fe at T ¼ 300, 150, and 12 K, in an attempt to characterize further the structure of these oxides. We see no evidence for a long-range magnetic ordering down to 12 K in

Electrical properties and Mössbauer spectra of rutile-type Fex/2Ta(Nb)x/2Ti1-xO2 (x = 0.05, 0.1) ceramics

“…A different C p (ω) behaviour of FTT01, sintered in CO 2 , is visible from Fig. 7(e), where C p (ω) also increases with temperature, but superposed humps are detectable at 500-600 K; the latter are reminiscent of maxima in C p (ω) vs. temperature data of relaxor ferroelectric-like rutile-type FeTiMO 6 (M= Ta,Nb) ceramics in the temperature range of 500-600 K [43,44,47,48], that were obviously to some part SE effects. For FNT005, sintered in air, Fig.…”

“…7(c) displays for FNT005 (air) a presentation of tan δ vs. frequency for various temperatures, whence for each temperature a low-and high-frequency peak is visible, arising from GB/SE and bulk relaxation processes, respectively. From these peaks, activation energies can be derived according to the relation f tanmax ∝ exp(−E Atan /k B T), with f tanmax the frequency at the maximum, E Atan the activation energy for a relaxation process to occur [41][42][43][44][45][46]. From data for several temperatures, E Atan =0.48 eV and 0.68 eV were deduced for bulk and GB/SE processes, respectively.…”

Dielectric and microwave properties study of TiFeNbO6 ceramics added Bi2O3

“…The rutile represents a generic inorganic structure adopted by several metal oxides of the MO 2 , MM 0 O 4 and the MM 0 2 O 6 stoichiometries [6]. Some of the authors have recently reported [5,7] strong relaxor ferroelectric behavior for the rutile based oxide, FeTiTaO 6 , which is comparable to the best relaxor materials, such as the Pb 3 MgNb 2 O 9 and the Pb 3 ZnNb 2 O 9 . The significant development of the lead-free relaxors [8,9], extended their investigation into the dielectric properties to several other MM 0 O 4 and MTiM 0 O 6 , for the M = Fe, Cr, Ga and the M 0 = Nb, Ta, Sb rutile-type oxides for a better understanding of the origin in the ferroelectric response of the rutile based oxides in general.…”

High temperature lead-free relaxor ferroelectric: Intergrowth Aurivillius phase BaBi2Nb2O9–Bi4Ti3O12 ceramics

“…5,6 Consequently, a great deal of effort has recently been put into exploring new RFE materials with higher T m value. [5][6][7][8][9][10][11][12] RFE exist in the different crystal structures that host ferroelectricity, including perovskites, tungsten bronzes, rutile structure, and Aurivillius phase. 7,8 In perovskites, RFE behavior occurs predominantly in lead-based complex compositions with the general formula Pb͑B 1 B 2 ͒O 3 , ͑B 1 =Mg 2+ ,Zn 2+ ,Ni 2+ ,Sc 3+ ..., B 2 =Nb 5+ ,Ta 5+ ,W 6+ ...͒ or lanthanum-substituted PbZr 1−x Ti x O 3 ͑PLZT͒.…”

“…21 Rutile-based FeTiTaO 6 is reported to be RFE with T m = 550 K at 530 Hz. 8 Aurivillius phase materials have generated increasing attention due to their potential use in nonvolatile ferroelectric random-access memory 22 and high-temperature piezoelectric applications. 23,24 Moreover, they are environment friendly lead-free piezoelectric materials.…”