UCLA

New routes to solid states materials are needed for discovery and the realization of improved reactions. By utilizing reactive approaches such as solid-state metathesis, pyrolysis, and nitride fluxes new routes to hard materials, phosphor hosts, and fast ion conductors were developed.

The fast ion conductor lithium silicon nitride, Li₂SiN₂, was produced in a metathesis reaction between silicon chloride, SiCl₄ and lithium nitride, Li₃N, initiated in a conventional microwave oven. The Li₂SiN₂ produced had a conductivity of 2.70 x 10^-3 S/cm at 500 °C.

Colorless millimeter-sized crystals of Ca₁₆Si₁₇N₃₄ were synthesized at high temperatures from a flux generated in situ from reaction intermediates. The compound was found to crystallize in the cubic space group F-43m (a = 14.8882 Å). The powder X-ray diffraction pattern of Ca₁₆Si₁₇N₃₄ matches that of a phase identified as cubic CaSiN₂ in the 1960s but never structurally characterized. In contrast to the orthorhombic phase of CaSiN₂, in which Ca²⁺ sits in octahedral sites, this cubic phase has Ca²⁺ in cubic sites that makes it an interesting host for new phosphors and gives rise to unique crystal field splitting.

A carbon-free silazane was formed by reacting metallic silicon in a melt of sodium amide; pyrolysis of this material offers a convenient route to Si₃N₄. The use of oxides for solid-state metathesis reactions was investigated for the formation of ternary silicon nitrides for phosphor hosts. Red, green, and blue phosphors were rapidly produced using rare earth oxides dopants. Solid-state metathesis reactions were investigated for the production of nano-scale B₄C and ZrC. The addition of a refractory, hard material significantly improves the mechanical properties of existing thermoelectric materials.