Synthesis of strontium bismuth niobate (SrBi2Nb2O9) using an aqueous acetate–citrate precursor gel: thermal decomposition and phase formation

Abstract

An aqueous solution gel route was developed for the preparation of the ferroelectric material strontium bismuth niobate (SrBi 2 Nb 2 O 9 ). Starting from aqueous Bi 3+ -acetate and Sr 2+ -acetate solutions and an aqueous peroxo-citrato-Nb 5+ -precursor solution, this method offers a low-cost and environmentally friendly alternative to the conventional sol-gel techniques. With regard to the deposition of thin films, it is important to gain insight in the behaviour of the precursor during thermal treatment. For this reason the thermal decomposition mechanism of the precursor gel was studied: weight loss and evolved gases were characterized by (hyphenated)TGA-MS and TGA-FTIR, while changes in the solid state during heating were detected using HT-DRIFT. The decomposition in dry air can be divided in four temperature regions. The first two steps are ascribed to the drying of the sample and to the decomposition of the organic matrix, not coordinated to the metal ions. During the third step the coordination sphere of the metal ions is decomposed and finally the residual organic matter is combusted in the fourth region.TEM experiments on freestanding thin films showed that the precursor homogeneity was maintained throughout the entire thermo-oxidative decomposition of the gel.The phase formation of SBN was studied by means of HT-XRD. At about 425 °C the intermediate fluorite phase is crystallized out of the amorphous precursor. The phase transformation into the desired ferroelectric perovskite phase seems to be dependent on the Bicontent: an excess of Bi lowers the onset temperature of perovskite formation.

Dielectric Relaxation Phenomenon in Ferroelectric Perovskite-related Structures

“…i) marked frequency dispersion in the vicinity of temperature (T m ) where the real part of the dielectric permittivity (ε') shows its maximum value, ii) the temperature of the corresponding maximum for ε' and the imaginary part of the dielectric permittivity (ε'') appears at different values, showing a frequency dependent behavior, iii-the Curie-Weiss law is not fulfilled for temperatures around T m . The materials have attracted considerable attention due to their large remanent polarization, lead-free nature, relatively low processing temperatures and other characteristics (Miranda et al, 2001;Kholkin et al, 2001;Lee et al, 2002;Nelis et al, 2005;Huang et al, 2006;Watanabe et al, 2006). The origin of the relaxor behavior for these materials has been associated to a positional disorder of cations on A or B sites of the perovskite blocks that delay the evolution of long-rage polar ordering (Miranda et al, 2001).…”

“…It has been previously commented that SrBi 2 Nb 2 O 9 is a member of the Aurivillius family (Blake et al, 1997;Ismunandar & Kennedy, 1999;Haluska & Misture, 2004;Nelis et al, 2005;Huang et al, 2006), consisting of octahedra in the perovskite blocks sandwiched by two neighboring (Bi 2 O 2 ) 2+ layers along the c-axis in a unit cell. The divalent Sr 2+ cation located between the corner-sharing octahedra can be totally or partially replaced by other cations, most commonly barium (Haluska & Misture, 2004;Huang et al, 2006).…”

Aqueous solution–gel preparation of ultrathin ZrO2 films for gate dielectric application

“…The thermo-oxidative decomposition of citratoperoxo-gels has been studied in detail by our group for different multimetal ion gel precursors [20][21][22]. The decomposition scheme with increasing temperature generally consists of a drying step (~100°C), followed by decomposition of the excess of ammonium citrate (~190°C), the pyrolysis of the complex (~350°C) and finally the removal of an organic rest fraction or carbonates (> 450°C).…”

“…scheme of aqueous citrato(peroxo) gels [19][20][21], at this temperature organic rest fractions are decomposed. These rest fractions are formed from the decomposition of excess ammonium citrate and consist of nitrogen containing organic compounds with a high thermal stability [20].…”

Structural, dielectric and piezoelectric properties of SrBi2Nb2O9 and Sr0.8Bi2.2Nb2O9 ceramics

“…Bi-layer structured compounds are generally represented by the following formula: (Bi 2 O 2 ) 2 þ (A nÀ 1 B n O 3n þ 1 ) 2 À , where A is Bi 3 þ , Ba 2 þ , Sr 2 þ , Ca 2 þ , Pb 2 þ , K þ or Na þ and B is Ti 4 þ , Nb 5 þ , Ta 5 þ , Mo 6 þ , W 6 þ or Fe 3 þ . A is the cation of coordination 12 in the perovskite sublattice which are octahedrally coordinated in perovskite layers, interleaved with (Bi 2 O 2 ) 2 þ layers and n is the number of perovskite layers and can be 1, 2, 3, 4, 5, or 8 [11]. Strontium bismuth niobate (SBN) and strontium bismuth tantalite (SBT) are the most important candidates among the members of Aurivillius family for the application in NVFRAM to replace lead zirconate titanate (PZT) in Ferroelectric random access memory (FeRAMs) application.…”