Ferroelectricity Driven by Twisting of Silicate Tetrahedral Chains

Abstract

Conventional perovskite-type ferroelectrics are based on octahedral units of oxygen, and often comprise toxic Pb to achieve robust ferroelectricity. Here, we report the ferroelectricity in a silicate-based compound, Bi 2 SiO 5 (BSO), induced by a structural instability of the corresponding silicate tetrahedral chains. A low-energy phonon mode condenses at ~ 673 K to induce the proper ferroelectric phase transition. Polarization switching was observed in a BSO single crystal with a coercive field of 30 kV/cm and a spontaneous polarization of 0.3 μC/cm 2 along a direction normal to the cleavage plane. The in-plane polarization was estimated by first principles calculations to be 23 μC/cm 2 . The present findings provide a new guideline for designing ferroelectric materials based on SiO 4 tetrahedral units, which is ubiquitously found in natural minerals.Because of its diverse functionality, ferroelectricity is a key ingredient for electronic and optical technologies applied to non-volatile memory, actuators and sensors. (1) Ferroelectric materials are characterized by a switchable polarization caused by spontaneous displacements of cations relative to anions, which generally appears through the ferroelectric phase transition from centrosymmetric to non-centrosymmetric phases. In the case of so-called displacive-type phase transitions, the phase transition is driven by the freezing of a zone-centre optical phonon mode, "soft mode", using an eigenvector similar to the polar displacement observed in the ferroelectric phase. (2-4) 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. (5-7) Current ferroelectric applications thus rely heavily upon toxic Pbbased compounds, because the large covalency of Pb-O is favourable for causing structural instability in these compounds to induce robust ferroelectricity. Alternately, the unconventional ferroelectricity observed in Bi-based perovskite-type oxides like BiFeO 3 (BFO), has recently attracted attention in terms of the high-T c and the large spontaneous polarization achieved without Pb. The mechanism has been understood as a lone-pair ordering, where the 6s orbital of Bi hybridizes with the 2p-orbital of an adjacent oxygen to induce the large polar displacement of Bi. (8,9) Also in this case, the ferroelectricity stems from the unique property of the specific element, Bi. Such a strong element-dependence of current ferroelectric oxides provides a demand for a new guideline principle for designing ferroelectric materials. (10,11)Here, we report for the first time the ferroelectric phase transition driven by the structural instability of the pyroxene-type one-dimensional chains of oxygen tetrahedra, which is found in the silicate-based compound Bi 2 SiO 5 (BSO). BSO has a layered structure, which comprises a single layer of one-dimensional silicate chains sandwiched between Bi 2 O 2 sheets (Fig. 1a). The proper ferroelectric phase transit...

Weak Ferroelectricity in n = 2 Pseudo Ruddlesden–Popper-Type Niobate Li2SrNb2O7

“…The Y-point softmode, on the other hand, induces the phase transition into non-polar Pmcn structure, which satisfies a necessary condition for the antiferroelectric phase transition. The calculated phonon dispersion thus indicates the close competition between ferroelectric and anti-ferroelectric instabilities in LSNO similarly to the case of Bi2SiO5 [32,32]. Since the present x-ray diffraction measurements have clarified the appearance of super structure reflections at Tc, the C-centered lattice can be automatically ruled out from candidates for the crystal symmetry below Tc as discussed in the preceding section.…”

Hierarchical dielectric orders in layered ferroelectrics Bi2SiO5

“…Bi 2 SiO 5 (BSO) has attracted much attention as an alternative to the traditional lead-based ferroelectric materials with a phase-transition temperature (T c ) of 673 K. BSO has an Aurivillius-like structure consisting of the [Bi 2 O 2 ] 2+ layer and [SiO 3 ] 2À layer ( Fig. 1a) (Pirovano et al, 2001;Georges et al, 2006;Taniguchi et al, 2013). A relatively large spontaneous polarization (P c ) of 14.5 mC cm À2 along the SiO 3 chain (c-axis) was predicted by first-principles calculations, while those along the a-and b-axes, P a and P b , are estimated to be small, 0.1 mC cm À2 and 0 mC cm À2 , respectively (Taniguchi et al, 2013).…”

“…1a) (Pirovano et al, 2001;Georges et al, 2006;Taniguchi et al, 2013). A relatively large spontaneous polarization (P c ) of 14.5 mC cm À2 along the SiO 3 chain (c-axis) was predicted by first-principles calculations, while those along the a-and b-axes, P a and P b , are estimated to be small, 0.1 mC cm À2 and 0 mC cm À2 , respectively (Taniguchi et al, 2013). From experimental P versus E measurements (Taniguchi et al, 2013), only the P a value of 0.8 mC cm À2 was detected, because the BSO crystals have a thin-plate shape, and the electrode for the P versus E measurements can only be formed on a large area of the b-c plane of the crystals.…”

Transformation of Perovskite BaBiO3 into Layered BaBiO2.5 Crystals Featuring Unusual Chemical Bonding and Luminescence

“…[14][15][16][17][18][19][20][21][22][23][24] One of the best examples is the topotactic conversiono fp erovskiteS rFeO 3 to layered SrFeO 2 with drastic changesi nl attice and magnetic properties. [25][26][27][28] Therefore, so far the structural and physicalp roperties of oxygen-poor derivatives of BaBiO 3 have remained poorly understood.I nspired by the discovery of superconductivity in hole-doped BaBiO 3 ,w eh ypothesized that new physical characteristics could exist in its oxygen-deficient phases that have new Bi coordination geometry and unusual chemicalbonding. [25][26][27][28] Therefore, so far the structural and physicalp roperties of oxygen-poor derivatives of BaBiO 3 have remained poorly understood.I nspired by the discovery of superconductivity in hole-doped BaBiO 3 ,w eh ypothesized that new physical characteristics could exist in its oxygen-deficient phases that have new Bi coordination geometry and unusual chemicalbonding.…”

“…[16] However, synthesis of BaBiO 3 -derivedp hases by oxygen removalh as proved challengingo wing to the difficulty in tuning oxygen stoichiometry in aw ell-controlled manner,a nd previous works commonlyl ed to the formation of mixed phases, which makes structural analysis and property characterization extremelyd ifficult. [25][26][27][28] Therefore, so far the structural and physicalp roperties of oxygen-poor derivatives of BaBiO 3 have remained poorly understood.I nspired by the discovery of superconductivity in hole-doped BaBiO 3 ,w eh ypothesized that new physical characteristics could exist in its oxygen-deficient phases that have new Bi coordination geometry and unusual chemicalbonding.…”