Piezoelectric LiTaO3 Research Articles

Analysis of longitudinal leaky surface acoustic waves on piezoelectric thin plates bonded to diamond substrate

Using the finite element method, we analyzed the resonance properties of a longitudinal leaky surface acoustic wave (LLSAW) on the structure of a piezoelectric LiTaO3 (LT) or LiNbO3 (LN) thin plate bonded to a diamond support substrate. When the plate thickness was 0.3 wavelength or larger, the particle displacements of the LLSAW were substantially concentrated near the surface, and the resonance properties were significantly improved compared to those of the single LT or LN. However, spurious responses due to other SAW modes also emerged. Regarding the LN thin plate, we obtained a phase velocity and fractional bandwidth of approximately 7300 m s−1 and 9.4%, respectively. Furthermore, a structure was proposed to suppress spurious responses in which the piezoelectric thin plate is divided into two layers with different Euler angles. The spurious responses were significantly suppressed after dividing the thin plate, while the main response of the LLSAW was maintained.

Surface Coupling between Mechanical and Electric Fields Empowering Ni-Rich Cathodes with Superior Cyclabilities for Lithium-Ion Batteries.

Ni‐rich cathodes with high energy densities are considered as promising candidates for advanced lithium‐ion batteries, whereas their commercial application is in dilemma due to dramatic capacity decay and poor structure stability stemmed from interfacial instability, structural degradation, and stress–strain accumulation, as well as intergranular cracks. Herein, a piezoelectric LiTaO3 (LTO) layer is facilely deposited onto Li[Ni x CoyMn1− x − y ]O2 (x = 0.6, 0.8) cathodes to induce surface polarized electric fields via the intrinsic stress–strain of Ni‐rich active materials, thus modulating interfacial Li+ kinetics upon cycling. Various characterizations indicate that the electrochemical performances of LTO‐modified cathodes are obviously enhanced even under large current density and elevated temperature. Intensive explorations from in situ X‐ray diffraction technique, finite element analysis, and first‐principle calculation manifest that the improvement mechanism of LTO decoration can be attributed to the enhanced structural stability of bulk material, suppressed stress accumulation, and regulated ion transportation. These findings provide deep insight into surface coupling strategy between mechanical and electric fields to regulate the interfacial Li+ kinetics behavior and enhance structure stability for Ni‐rich cathodes, which will also arouse great interest from scientists and engineers in multifunctional surface engineering for electrochemical systems.

Surface Stabilization of Ni-Rich Layered Cathode Materials via Surface Engineering with LiTaO3 for Lithium-Ion Batteries.

Recently, Ni-rich layered cathode materials have become the most common material used for lithium-ion batteries. From a structural viewpoint, it is crucial to stabilize the surface structures of such materials, as they are prone to undesirable side reactions and particle cracking in which intergranular microcracks form at the particle surfaces and then propagate inside. As a simplified engineering technique for obtaining Ni-rich cathode materials with high reversibility and long-term cycling stability, we propose a facile surface coating of piezoelectric LiTaO3 onto a Ni-rich cathode material to enhance the charge transfer reaction and surface structural integrity. Based on theoretical and experimental investigation, we demonstrate that this surface protection approach is effective at enhancing the reversibility and mechanical strength of Ni-rich cathode materials, leading to a stable cycle performance at up to 150 cycles, even at 60 °C. Furthermore, the piezoelectric characteristics of the surface LiTaO3 can enhance the rate capability of Ni-rich cathode materials at current densities of up to 2.0C. The results of this study provide a practical insight on the development of Ni-rich cathode materials for practical use in electric vehicle applications.

Solid-state self-template synthesis of Ta-doped Li2ZnTi3O8 spheres for efficient and durable lithium storage

SummaryTa-doped Li2ZnTi3O8 (LZTO) spheres (Li2ZnTi3-xTaxO8; where x is the synthetic chemical input, x = 0, 0.03, 0.05, 0.07) are synthesized via solid-state reaction using mesoporous TiO2 spheres as the self-template. The majority of Ta5+ ions are uniformly doped into crystal lattices of LZTO through the Ti↔Ta substitution, and the rest forms the piezoelectric LiTaO3 secondary phase on the surface, as confirmed by X-ray diffraction refinement, Raman spectroscopy, density functional theory, and electron microscopy. Electrochemical impedance spectroscopy demonstrates that the Ta5+ doping creates rapid electronic transportation channels for high Li+ ion diffusion kinetics; however, the LiTaO3 surface coating is beneficial to improve the electronic conductivity. At the optimal x = 0.05, Li2ZnTi3-xTaxO8 spheres exhibit a reversible capacity of 90.2 mAh/g after 2000 cycles with a high coulombic efficiency of ≈100% at 5.0 A/g, thus enabling a promising anode material for lithium-ion batteries with high power and energy densities.

Local Electric-Field-Driven Fast Li Diffusion Kinetics at the Piezoelectric LiTaO3 Modified Li-Rich Cathode-Electrolyte Interphase.

As one of the most promising cathodes for next‐generation lithium ion batteries (LIBs), Li‐rich materials have been extensively investigated for their high energy densities. However, the practical application of Li‐rich cathodes is extremely retarded by the sluggish electrode–electrolyte interface kinetics and structure instability. In this context, piezoelectric LiTaO3 is employed to functionalize the surface of Li1.2Ni0.17Mn0.56Co0.07O2 (LNMCO), aiming to boost the interfacial Li+ transport process in LIBs. The results demonstrate that the 2 wt% LiTaO3‐LNMCO electrode exhibits a stable capacity of 209.2 mAh g−1 at 0.1 C after 200 cycles and 172.4 mAh g−1 at 3 C. Further investigation reveals that such superior electrochemical performances of the LiTaO3 modified electrode results from the additional driving force from the piezoelectric LiTaO3 layer in promoting Li+ diffusion at the interface, as well as the stabilized bulk structure of LNMCO. The supplemented LiTaO3 layer on the LNMCO surface herein, sheds new light on the development of better Li‐rich cathodes toward high energy density applications.

Surface energy engineering for LiTaO3 and α-quartz SiO2 for low temperature (<220 °C) wafer bonding

Wafer bonding can be substituted for heteroepitaxy when manufacturing specific heterojunction-based devices. Devices manufactured using wafer bonding include multijunction solar cells, integrated sensors, heterogeneously integrated photonic devices on Si (such as high-performance laser diodes), Mach-Zehnder modulators, photodetectors, optical filters, and surface acoustic wave devices. In these devices, creating heterointerfaces between different semiconductors with heavily mismatched lattice constants and/or significant thermal expansion mismatch presents significant challenges for heteroepitaxial growth. High costs and poor yields in heavily mismatched heteroepitaxy can be addressed by wafer bonding in these optoelectronic devices and sensors, including the LiTaO3/Si and LiTaO3/SiO2 heterostructures. In the present work, heterostructure formation between piezoelectric LiTaO3 (100) and Si (100) and α-quartz SiO2 (100) is investigated via wafer bonding. Direct bonding is selected instead of heteroepitaxy due to a significant thermal expansion mismatch between LiTaO3 and Si-based materials. The coefficient of thermal expansion (CTE) of LiTaO3 is 18.3 × 10−6/K. This is 1 order of magnitude larger than the CTE for Si, 2.6–2.77 × 10−6/K and 25–30 times larger than the CTE for fused SiO2 and quartz (which ranges 0.54–0.76 × 10−6/K). Thus, even at 200 °C, a 4 in. LiTaO3/Si bonded pair would delaminate with LiTaO3 expanding 300 μm in length while Si would expand only by 40 μm. Therefore, direct wafer bonding of LiTaO3/Si and LiTaO3/SiO2 is investigated with low temperature (T < 500 K) Nano-Bonding™, which uses surface energy engineering (SEE). SEE is guided by fast, high statistics surface energy measurements using three liquid contact angle analysis, the van Oss/van Oss–Chaudhury–Good theory, and a new, fast Drop Reflection Operative Program analysis algorithm. Bonding hydrophobic LiTaO3 to hydrophilic Si or SiO2 is found to be more effective than hydrophilic LiTaO3 to hydrophobic Si or SiO2 temperatures for processing LiTaO3 are limited by thermal decomposition LiTaO3 into Ta2O5 at T ≥ 180 °C due to Li out-diffusion as much as by LiTaO3 fractures due to thermal mismatch.

Hyper frequency modeling of resonated systems based on piezoelectric LiTaO3 thin layers

In this work, we discuss the piezoelectric activity of lithium tantalite (LiTaO3) thin layers and to more understand this phenomenon we have developed a model for our LiTaO3 resonators based on mason model and simulated the hyper frequency behavior. Our LiTaO3 resonators are made from three layers staked on silicon substrates. The aluminum thin film constitutes the external electrode, the platinum forms the internal electrode and the lithium tantalite constitutes the piezoelectric layer. Each element of these layers is represented by an arrangement of impedances. The simulation shows the reflection coefficient, ρ, as a function of the frequency. We observe a resonant frequency that decreases with the increase of the thickness of the piezoelectric LiTaO3 layers. A slight variation of this resonant frequency is obtained when comparing it with that of the uncharged piezoelectric device, which is due to the different layers loading the system. Over oscillations superposing to the envelope are observed and found to be related to the propagation of the acoustic wave in the silicon substrate. From these over oscillations one can see that this system can be used as an efficient method to calculate the thickness of any substrate.

Microstructure and Toughening Mechanisms in an Al<sub>2</sub>O<sub>3</sub> Ceramic Matrix Composite Dispersed with LiTaO<sub>3</sub> Particles

LiTaO3 (5--25vol%) dispersed Al2O3 matrix composite (LTA) with high relative density were fabricated by hot pressing at 1300°C. The microstructure and mechanical properties of the composite were studied. The main results are as follows: Al2O3 was found to be phase compatible with piezoelectric LiTaO3 during high temperature sintering process. The relative density of the LTA composites was greatly improved by the addition of LiTaO3 particles. Domains are clearly discerned in LiTaO3 grains in the LTA composite, confirming that LiTaO3 particles remain ferroelectrics. 90 degree domains were observed in LiTaO3 grains constrained strongly by Al2O3 matrix, which has never been found in LiTaO3 single crystal before. Comparing with those of pure Al2O3, sintered at same temperature (1300°C), both the flexural strength and the fracture toughness of the composites are all enhanced. Domain switching is suggested as a new toughening mechanism in the ferroelectric particles dispersed structural ceramics.