In this work, the high-yield synthesis of BaTi 2 O 5 (BT2) nanorods with a growth direction at [020] was achieved in the medium of KCl salt through the molten-salt synthesis (MSS) with Ba(NO 3 ) 2 and anatase TiO 2 as reactants. By optimizing the involved reaction factors including particle sizes, thermal holding durations and crystalline forms of TiO 2 , ultra-pure BT2 nanorods with uniform size were obtained after 45 min of heating at 950 °C. Meanwhile, anatase and rutile TiO 2 were respectively mixed and calcined in KCl to study the formation and transformation process of BT2 nanorods in detail. It was found that anatase TiO 2 tends to merge together and convert into rutile TiO 2 . In particular, the formed rutile TiO 2 reacts with BaO and BaTiO 3 to spontaneously form BT2 nanorods without any presence of rod-like templates. Besides, BT2 takes priority over K 2 Ti 6 O 13 to generate the corresponding nanorods in the molten salt with high content of K + . In addition, the O 2 in air also promotes the formation of nanorods. According to the experimental results, a probable mechanism for the initial formation, subsequent growth and transformation of BT2 nanorods was thus proposed, which helps to facilitate the preparation of BT2-based one-dimensional nanomaterials.
Flexible piezoelectric energy harvesters (PEHs) have gained substantial attention owing to their wearability, breathability, and sustainable self-powered supply. However, existing film PEHs cannot identify forces in different bending directions, limiting their applications in wearable electronics and artificial intelligence. This study constructs a fabric PEH for the first time by introducing piezoelectric anisotropic BaTi 2 O 5 nanorods (BT2-nr) into piezoelectric polyvinylidene fluoride (PVDF) nanofibers with a bi-oriented architecture, in which BT2-nr uniformly aligns in the PVDF nanofiber during electrospinning. The dual-orientation feature endows the flexible PEH with anisotropy, which can sensitively identify the forces at different bending directions (e.g., bent vertically, parallelly, or twisted by 45° along the fiber orientations). Simultaneously, the composite PVDF/BT2 PEH containing 15 wt.% BT2-nr delivers an optimal piezoelectric output of 31.2 V with a high sensitivity of 5.22 V N −1 . The developed anisotropic PEH can be used as a self-powered pressure sensor for multimodal intelligent biomonitoring of human movement. This study provides a feasible strategy for fabricating self-powered flexible PEHs with high electromechanical conversion efficiency and multifunctionality for wearable piezoelectric pressure sensors.
Piezoelectric energy harvesters (PEHs) with a three-dimensional (3D) structure are arousing increasing interest because of the ability to efficiently convert mechanical energy into electricity catering for self-powered systems. Among them, 3D PEHs composed of 1–3-type piezoelectric composites which exploit one-dimensional (1D) piezoceramic fillers rather than conventional powders are particularly attractive. However, an issue involving the orientation of the 1D fillers to utilize the piezoelectric effect renders the 3D structural design for high-efficiency energy conversion more challenging. Herein, for the first time, we introduce the fused deposition modeling (FDM) 3D printing to the flexible construction of poly(vinylidene fluoride) (PVDF)-based 3D PEHs by incorporating 1D BaTi2O5 (BT2) nanorods as piezoelectric fillers. The shearing force generated by FDM successfully realizes the in situ uniform orientation of BT2 nanorods in the PVDF (98% β crystals) matrix along the nozzle extrusion direction. Besides, by coupling 3D printing with the appealing piezoelectric anisotropy feature of BT2 nanorods, the 3D PEH is able to generate different piezoelectric responses to the same applied external force from X, Y, and Z directions. Furthermore, an optimized 3D conical array structure is constructed to amplify the effective deformation of the PEH to enhance its piezoelectric output. As expected, customized PEH can continuously power commercial electronic devices and monitor various human motions, indicating 3D printing as a multifunctional strategy to fabricate 3D PEHs with 1–3-type piezoelectric composite materials for self-powering microelectronic applications.
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