Effects of Size and Structural Defects on the Vibrational Properties of Lanthanum Hexaboride Nanocrystals

Lanthanum hexaboride (LaB₆) is notable for its thermionic emission and mechanical strength and is being explored for its potential applications in IR-absorbing photovoltaic cells and thermally insulating window coatings. Previous studies have not investigated how the properties of LaB₆ change on the nanoscale. Despite interest in the tunable plasmonic properties of nanocrystalline LaB₆, studies have been limited due to challenges in the synthesis of phase-pure, size-controlled, high-purity nanocrystals without high temperatures or pressures. Here, we report, for the first time, the ability to control particle size and boron content through reaction temperature and heating ramp rate, which allows the effects of size and defects on the vibrational modes of the nanocrystals to be studied independently. Understanding these effects is important to develop methods to fully control the properties of nanocrystalline LaB₆, such as IR absorbance. In contrast to previous studies on stoichiometric LaB₆ nanocrystals, we report here that boron content and lanthanum vacancies have a greater influence on their vibrational properties than their particle size

Evolution of Vibrational Properties in Lanthanum Hexaboride Nanocrystals

Lanthanum hexaboride (LaB₆) is known for its hardness, mechanical strength, thermionic emission, and strong plasmonic properties. However, given the lack of colloidal synthetic methods to access this material, very little is understood about its physical properties on the nanoscale. Recently, a new moderate-temperature synthetic technique was developed to directly synthesize LaB₆ nanoparticles [Mattox et al. Chem. Mater. 2015, 27, 6620]. We report the influence of nanoparticle size on the structural and vibrational properties of LaB₆ using a combination of Raman and Fourier transform infrared spectroscopies. Our studies indicate that the size of the lanthanum salt anion has a larger influence on LaB₆ vibrational energies than particle size. Surprisingly, our work finds that the LaB₆ lattice readily expands to accommodate larger ions and contracts with their removal, while ligand incorporation significantly amplifies and shifts the Raman stretching modes

Monodisperse Sn Nanocrystals as a Platform for the Study of Mechanical Damage during Electrochemical Reactions with Li

Monodisperse Sn spherical nanocrystals of 10.0 ± 0.2 nm were prepared in dispersible colloidal form. They were used as a model platform to study the impact of size on the accommodation of colossal volume changes during electrochemical lithiation using ex situ transmission electron microscopy (TEM). Significant mechanical damage was observed after full lithiation, indicating that even crystals at these very small dimensions are not sufficient to prevent particle pulverization that compromises electrode durability