Ferroelectricity Driven by Twisting of Silicate Tetrahedral Chains

Abstract

Because of its diverse functionality, ferroelectricity plays a key role in electronic and optical technologies. [1] Ferroelectric materials are characterized by a switchable polarization caused by spontaneous displacements of cations relative to anions, which occurs in centrosymmetric to noncentrosymmetric ferroelectric phase transitions. In the case of displacive-type phase transitions, the phase transition is driven by the freezing of a zone-center optical phonon mode, "soft mode", using an eigenvector similar to the polar displacement observed in the ferroelectric phase. [2] Recent studies have clarified that the soft mode instability in conventional perovskite-type oxides is caused by covalency between the cations and oxygen ions in the octahedral oxygen units. [3] Current ferroelectric applications rely heavily upon toxic Pb-based compounds, because the strong covalency of PbÀO causes structural instability in these compounds and induces the large spontaneous polarization. Alternately, Bibased perovskite-type oxides like BiFeO 3 (BFO), have recently attracted attention because of their high Curie temperature (T c ) and its large polarization that is comparable to the Pb-based ferroelectrics. [4] The 6s 1orbital of Bi hybridizes with the adjacent oxygen 2p orbital to induce the large polar displacement of Bi. [5] Also in this case, the ferroelectricity stems from the unique property of the specific element, Bi. Such a strong element dependence of ferroelectric oxides demands new principle guidelines for designing ferroelectric materials. [6] Here, we report for the first time the ferroelectric phase transition driven by the structural instability of pyroxenoidtype one-dimensional chains of oxygen tetrahedra, which occur in the silicate-based compound Bi 2 SiO 5 (BSO). BSO has a layered structure, which comprises a single layer of onedimensional silicate chains sandwiched between Bi 2 O 2 sheets (Figure 1 A). The ferroelectric phase transition at 663 K is induced by the freezing of the soft mode that stems from the twisting of silicate chains. The ferroelectricity is verified by a direct observation of the P-E hysteresis loops and arises from the structural instability of the tetrahedral oxygen chains. Therefore, the present finding offers a new route for designing environmentally friendly ferroelectric oxides that are free from specific element constraints.The crystal structure of BSO has previously been reported to be an orthorhombic Cmc2 1 at room temperature. [7] Our transmission electron microscopy (TEM) observations, however, reveal that the crystallographic b angle of BSO slightly deviates from 908 at room temperature, indicating a monoclinic distortion of BSO (see Figure S1 A in the Supporting Information). X-ray powder diffraction analysis indicates that BSO has a monoclinic Cc crystal structure with lattice parameters of a = 15.1193(1) , b = 5.4435(1) , c = 5.2892(1) , and b = 90.0695(20)8 ( Figure S2 A). At 793 K, the b angle changes to 908, demonstrating a structural phase transition from the monoc...

Weak ferroelectricity and low-permittivity microwave dielectric properties of Ba 2 Zn (1+x) Si 2 O (7+x) ceramics

“…These properties indicate that low permittivity can reduce reflection at the air-dielectric interface, minimise cross-coupling with conductors and accelerate electronic signal transition [6]. Furthermore, ferroelectric (FE) materials, especially the new environment-friendly FE oxides [1], can be regarded as voltage-controlled frequency-agile elements in tunable-microwave and millimetre-wave devices, such as capacitors, phase shifters and oscillators [14]. In addition, novel materials with both ferroelectricity and microwave dielectric properties can have other applications.…”

“…Low-cost silicates exhibit many interesting and important characteristics, such as ferroelectricity in Bi 2 SiO 5 and Ba 2 ZnSi 2 O 7 [1,2]; low-permittivity microwave dielectric properties in M 2 SiO 4 (M = Ba, Sr, Ca, Zn, Mg, Mn) [3][4][5], MSiO 3 (M = Hf, Mg, Ca) [6][7][8] and Ba 2 ZnSi 2 O 7 [2,9,10]; and a unique thermal expansion coefficient in barium zinc silicates [11][12][13].…”

Switchable Charge‐Transfer in the Photoelectrochemical Energy‐Conversion Process of Ferroelectric BiFeO3 Photoelectrodes

“…[5,6] The current approach for energy-conversion devices with traditional semiconductors, however, has two limits: 1) the photovoltage of the devices is limited by the band gap of the semiconductors employed ; 2) the charge-transfer direction is confined and fixed by the junctions of the semiconductor/semiconductor, semiconductor/metal or semiconductor/electrolyte.An alternative approach to overcome the limits of the common semiconductors is to fabricate solar-energy conversion devices with ferroelectric materials. Ferroelectric materials, typically BiFeO 3 (BFO) [7][8][9][10][11] and Pb(Zr,Ti)O 3 (PZT), [12][13][14] have a large, stable and tunable remnant ferro-electric polarization which produces a depolarization (internal) electric field extending over the whole film volume, giving the resulting devices high efficiency in separating photo-generated charges and switching charge-transfer directions. Therefore, Walsh et al [15] claimed that the excellent performance of Perovskite solar cells based on CH 3 NH 3 PbI 3 originated from the presence of ferroelectric domains in the Perovskite structure.…”

Switchable Charge‐Transfer in the Photoelectrochemical Energy‐Conversion Process of Ferroelectric BiFeO3 Photoelectrodes

“…An alternative approach to overcome the limits of the common semiconductors is to fabricate solar‐energy conversion devices with ferroelectric materials. Ferroelectric materials, typically BiFeO 3 (BFO)7–11 and Pb(Zr,Ti)O 3 (PZT),12–14 have a large, stable and tunable remnant ferroelectric polarization which produces a depolarization (internal) electric field extending over the whole film volume, giving the resulting devices high efficiency in separating photo‐generated charges and switching charge‐transfer directions. Therefore, Walsh et al 15.…”