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Outstanding Piezoelectric Performance in Lead-Free 0.95(K,Na)(Sb,Nb)O <sub/>3</sub> -0.05(Bi,Na,K)ZrO <sub/>3</sub> Thick Films with Oriented Nanophase Coexistence
摘要： Lead-free 0.95(K0.48Na0.52)(Nb0.95Sb0.05)O3-0.05Bi0.5(Na0.82K0.18)0.5ZrO3 (KNSN-BNKZ0.05) piezoelectric films with preferred crystal orientation and enhanced thickness are fabricated on silicon substrates from a chemical solution approach. Adequate K excess is introduced to obtain a single perovskite phase in the resulting thicker films. The effects of thickness, crystal orientation, and structure of the films on the performance are investigated. Outstandingly large effective piezoelectric strain coefficient up to 250 pm V?1 is demonstrated over a macroscopic scale using a laser scanning vibrometer in the [100]-KNSN-BNKZ0.05 film with an enhanced thickness of 2.7 μm, competitive to the benchmark oriented lead zirconate titanate films on silicon. Atomically resolved electron microscopy reveals the coexistence of oriented ferroelectric rhombohedral (R) and tetragonal (T) phases at the nanometer scale with gradual polarization rotation, which can lower the domain wall energy and facilitate the large piezoelectric response. The increased film thickness reduces the in-plane mechanical clamping to enable more free deformation in the thickness direction and improve domain wall mobility, both further contributing to enhanced piezoelectric response.
关键词： orientation,sodium potassium niobate,piezoelectric films,phase coexistence,lead-free electronics
更新于2025-09-19 17:15:36
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Investigations on electrical and thermal transport properties of Cu2SnSe3 with unusual coexisting nanophases
摘要： The ternary diamond-like compound Cu2SnSe3 is a potential thermoelectric material. Its Cu-Se conducting network leaves Sn as a likely doping site to optimize the carrier concentration without much deterioration to the carrier mobility. Thus, the precise determination on the intricate phase structures of Cu2SnSe3 is critical. Here, we first use the atomically resolved scanning transmission electron microscopy and reveal an unusual phase coexistence (monoclinic and orthorhombic phases) in Ag-doped Cu2SnSe3. Owing to coexisting phases and the orderedisorder transition in the orthorhombic phase, the Ag-doped Cu2SnSe3 shows an unusual three-stage behavior in its temperature-dependent electrical transport properties and achieves record high power factors in this system. The observed three-stage behavior due to the phase coexistence is supported by the first principle calculations, Hall measurements, and optical diffuse reflectance measurements. To fully understand the band structures and the coherent interface between these coexisting phases, a band contact model is proposed that could well explain the three-stage electrical transport behavior. Moreover, the phase coexistence is observed at the nanoscale regime, thus providing a high density of phase boundaries. Such coexisting nanophases play an important role in lowering the lattice thermal conductivity. As a result, the ZT value obtained in Cu2Sn0.93Ag0.07Se3 is double that of undoped Cu2SnSe3.
关键词： Diamond-like compound,Phase coexistence,Thermoelectric,Cu2SnSe3
更新于2025-09-04 15:30:14