Browsing by Author "Li, L"

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    One-Dimensional Piezoelectric BaTiO3 Polycrystal of Topochemical Mesocrystal Conversion from Layered H2Ti4O9·H2O Single Crystal
    (American Chemical Society, 2018) Hu, D; Miao, L; Zhang, Z; Li, L; Wang, Y; Hualei, C; Feng, Q; Fan, M; Zhao, L; Sewwandi, GA
    A one-dimensional (1D) piezoelectric BaTiO3(BT) polycrystal with a tetragonal system was controllably prepared using a one-step hydrothermal soft chemical process. A layered H2Ti4O9·H2O (HTO) single crystal was used as the precursor. Interestingly, the obtained polycrystalline BT constructed from oriented BT nanoparticles shows a set of single-crystalline diffraction points, implying that the BT polycrystal is a mesocrystal. The [010] and [001] directions of the obtained mesocrystalline BT correspond to the [001] and [010] directions of the original HTO crystal, respectively, and the [010] direction of the mesocrystalline BT corresponds to the direction along the length of a 1D rod matrix. An in situ topochemical mesocrystal conversion of mesocrystalline BT grown on the HTO substrate occurred not only on the substrate surface but also in the interlayers owing to the unique TiO6 octahedral layers of HTO. In addition, the piezoelectric response of the 1D mesocrystal was captured for the first time. The piezoelectric property of BT mesocrystals hinges on its nanostructure. It is a challenge to develop a special process to prepare highly 1D anisotropic perovskite titanate polycrystals with high crystallinity and piezoelectric response. This novel strategy can be utilized to develop piezoelectric mesocrystalline materials.
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    Rod-like incipient ferroelectric SrTiO3 polycrystal with crystal-axis orientation
    (Elsevier, 2020) Zhang, Z; Miao, L; Yao, M; Li, L; Zhao, F; Gu, H; Han, Y; Galhenage, AS; Feng, Q; Yang, D; Wang, X; Hu, D
    Strontium titanate (SrTiO3, ST) is an incipient ferroelectric material. Generally, a one-dimensional (1D) ST polycrystal is difficult to obtain because of its high aspect ratio and directional orientation. We prepared a 1D ST polycrystal from a layered H2Ti4O9·H2O (HT) single crystal via a solvothermal soft chemical process. The 1D ST polycrystal fabricated from ST nanocrystals has a [010] crystal axis, implying that it is a mesocrystal. The ST nanocrystals were grown not only on the surfaces but also in the interlayers of the original HT matrix. The formation mechanism of the ST mesocrystal is based on a topochemical mesocrystal conversion process. ST ceramics fabricated from ST mesocrystal powder present a lossy capacitor response and excellent energy-storage capabilities owing to the presence of locally oriented ST nanocrystals with a lattice mismatch in the rod-like ST mesocrystals. The investigations performed in this study can set a new benchmark for the development of new electric ST-based materials.
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    Solvothermal reaction and piezoelectric response of oriented KNbO3Polycrystals
    (ACS Publications, 2021) Yang, D; Wang, Y; Li, L; Yao, M; Zhang, W; Gu, H; Zhang, S; Fan, M; Sewvandi, GA; Hu, D
    KNbO3 (KN) piezoelectric polycrystals were prepared by a two-step solvothermal reaction process with the managed organic solvents as reaction mediums at a low temperature for a short time. In the solvothermal reaction system, the formation mechanism of polycrystalline KN is mainly the dissolution–deposition mechanism. The influences of alkalinity, viscosity, and the polarity for reaction mediums on the formation of the niobates were investigated. The chemical reaction mechanisms of niobate products and formation mechanism of niobate crystals from the precursor were clarified. The regulating and controlling mechanism of the phase compositions, the morphologies, and the lattice constants for the niobates obtained in varied reaction mediums were revealed. The obtained KN piezoelectric polycrystals are constructed from oriented KN nanocrystals. Piezoelectric hysteresis loops of cuboid KN polycrystals were detected for the first time. A prepared cuboid KN polycrystal shows an average d33* value of 32 pm/V. The study provides a strategy for the development of oriented KN piezoelectric materials to apply the orientation engineering.
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    Topochemical conversion of the discontinuous-zone-axis to form bismuth titanate oriented polycrystal nanocomposites
    (Royal Society of Chemistry, 2021) Wang, Y; Yang, D; Yao, M; Li, L; Huang, Z; Zhang, W; Han, Y
    Bismuth titanate based materials have wide potential applications in the fields of dielectrics, piezoelectrics, ferroelectrics, catalysis and energy storage. In this study, a two dimensional (2-D) layered H1.07Ti1.73O4·nH2O (HTO) crystal was used as a precursor to prepare 2-D bismuth titanate oriented polycrystal nanocomposites using two kinds of Bi3+ sources. The chemical reaction mechanisms for the formation of bismuth titanates are proposed, and the crystal structures and their conversions are also identified. The formation mechanism of the discontinuous-zone-axis is revealed. The obtained bismuth titanates are oriented polycrystals constructed from the orientation nanocrystals. In the process of forming the oriented polycrystal, the zone axis of the bismuth titanates obtained under different reaction conditions can vary even if the same reactants are used in the reaction. The certain topological correspondences among the oriented polycrystal, the precursor, and the intermediate, as well as the formation of bismuth titanates with a discontinuous-zone-axis based on a topochemical mesocrystal conversion reaction, were proposed. The special arrangement structure of the TiO6 octahedral layers accommodating in the HTO crystal is the main reason for the constant change of the zone axis of the bismuth titanate nanocomposite. However, based on the crystallographic investigation of the reaction mechanism involved in the formation process of construction of the bismuth titanate oriented polycrystal nanocomposite from the HTO crystal, it is found that the topochemical mesocrystal conversion reaction with a discontinuous-zone-axis is different from the conventional topochemical reactions. This may be attributed to the combination of the HTO matrix and Bi3+. It is vital to study the controllable preparation of bismuth titanate based nanocomposites and further understand the topochemical reaction.