Abstract
Bronze phase titanium dioxide (TiO2-B) has an ideal open structure for applications in high-rate lithium-ion batteries, but high quality and water-free TiO2-B is difficult to synthesize since TiO2-B is energetically less stable compared to other TiO2 polymorphs. Using CaTi5O11 as a template layer can help stabilize TiO2-B phase, but it is still challenging to avoid the formation of TiO2 anatase (TiO2-A) impurity phase. Here we show the synthesis of phase pure TiO2-B films by in situ engineering of the surface quality of the buffer layer using molecular beam epitaxy (MBE). By applying surface sensitive in situ reflection high-energy electron diffraction (RHEED), the formation of the impurity TiO2 anatase phase on the surface of CaTi5O11 buffer layer can be monitored and eliminated in real time, leaving a clean template surface for the growth of phase pure TiO2-B films.
Highlights
Titanium dioxide has four major different polymorphs: rutile, anatase, brookite, and bronze, and they have wide applications in photocatalysis,1,2 memory devices,3,4 solar cell,5 dilute ferromagnetic oxides,6–8 and lithium-ion batteries.9,10 Especially for the bronze phase of titanium dioxide, the open structure and fast lithium-ion transport via a pseudocapacitive Faradaic process can lead to ultrahigh discharge rate compare to those of supercapacitors,11 which is promising for high performance energy applications
CaTi5O11 is very sensitive to the exact growth condition and slight deviation from the optimal growth condition will lead to TiO2 anatase (TiO2-A) impurity phase
In this letter we show that phase-pure TiO2 films can be synthesized by molecular beam epitaxy (MBE)
Summary
Titanium dioxide has four major different polymorphs: rutile, anatase, brookite, and bronze, and they have wide applications in photocatalysis, memory devices, solar cell, dilute ferromagnetic oxides, and lithium-ion batteries. Especially for the bronze phase of titanium dioxide, the open structure and fast lithium-ion transport via a pseudocapacitive Faradaic process can lead to ultrahigh discharge rate compare to those of supercapacitors, which is promising for high performance energy applications. For the bronze phase of titanium dioxide, the open structure and fast lithium-ion transport via a pseudocapacitive Faradaic process can lead to ultrahigh discharge rate compare to those of supercapacitors, which is promising for high performance energy applications. TiO2-B was mainly synthesized in nanostructures by hydrothermal methods and products often contain unreacted precursors, other TiO2 phases, and the unavoidable presence of structural water.. TiO2-B was mainly synthesized in nanostructures by hydrothermal methods and products often contain unreacted precursors, other TiO2 phases, and the unavoidable presence of structural water.9,12–16 This hinders the understanding of the intrinsic properties and further applications of this compound. These TiO2-B like slabs provide a template for subsequent growth of TiO2-B film. Since deposing TiO2 on this mixed surface will form TiO2-A impurity phase, it is still extremely challenging to synthesis phase-pure TiO2-B films
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