Determining the Location and Role of Al in Al-Modified TiO₂ Nanoparticles Using Low-Temperature Heat Capacity, Electron Energy-Loss Spectroscopy, and X-ray Diffraction

Abstract

The location and function of dopants in metal oxide nanoparticles have been poorly characterized for many systems. We have performed heat capacity measurements, electron energy-loss spectroscopy (EELS), and X-ray diffraction (XRD) on ten TiO 2 nanoparticle samples that have different amounts of Al dopant to determine the location and function of the Al 3+ cations. From the heat capacity data, lattice vacancies are observed to increase significantly with the addition of the Al dopant, suggesting Al 3+ cations enter the TiO 2 lattice and create vacancies due to the charge difference between Al 3+ and Ti 4+ . The presence of gapped terms in fits of the low-temperature heat capacity data also suggests that small regions of short-range order are created within the TiO 2 lattice. Entropies at T = 298.15 K were determined from the heat capacity data and show effects related to the entropy of mixing, suggesting that a solid solution of Al/TiO 2 is formed. EELS data confirm that Al enters the TiO 2 lattice but also indicates that the short-range structure around the Al atoms shifts from a TiO 2 -like environment towards an Al 2 O 3 -like environment as the dopant concentration increases. XRD data suggest that the long-range order of the particles decreases as the dopant concentration increases but retains a basic TiO 2 -like structure. This is the first investigation to use heat capacity data in this manner to determine the location of the dopant.

Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

“…The heat capacity data showed that lattice vacancies increased significantly with the addition of the Al dopant, suggesting that the Al 3+ cations entered the titania lattice and created vacancies due to the charge difference between Al 3+ and Ti 4+ . 485 Crozier and colleagues used monochromated EELS-STEM to measure bandgap states in individual non-stoichiometric praseodymium-ceria NPs. The authors of that study reported that the combination of EELS and AC-STEM offers new opportunities for the local nanoscale probing of bandgap states, and correlation with structure and chemistry at the 0.1 nm level.…”

Electron Microscopy Studies of Soft Nanomaterials

“…Using Al-doped TiO 2 NPs as an example, EELS spectra confirmed the entering of Al atoms into TiO 2 lattice, as well as the transition of local structure around Al atoms from a TiO 2 -like environment to an Al 2 O 3 -like environment as the dopant concentration increases. 104 The observation of the transition was realized through the comparison of EELS data of samples to the Al 2 O 3 standard one.…”

Relaxation calorimetry and its application in low temperature specific heat study of solids

“…x=0.0, 0.2, 0.5, 0.8, 1.0)样品1.9~300 K比 热, 插图为20 K以下曲线 [40] (网络版彩图) 火材料等 [47] . 52] 使用PPMS和DSC研究了1.9~400 K温区摩尔质量 图 9 PPMS测定的1.9~300 K纯的和Al掺杂的TiO 2 纳米颗粒 的摩尔比热 [45] (网络版彩图) Figure 9 Molar heat capacity data from 1.9-300 K measured on a quantum design PPMS of pure and Al doped TiO 2 nanoparticles [45] (color online).…”

“…图 10 纯的和Al掺杂的TiO 2 纳米颗粒1.9~10 K低温摩尔比 热(C/T-T图) [45] (网络版彩图) [52] (网络版彩图) (网络版彩图) Figure 13 Plot of the experimental heat capacities of BS-T (T=400, 500, 600, and 800) samples measured over the temperature range from 2 to 300 K. Insets show the data below T=10 K [59] (color online).…”

“…Low temperature heat capacity data from 1.9-10 K of pure and Al doped TiO 2 nanoparticles plotted as C/T versus T[45] (color online).…”