Preparation and properties of carbonyl iron particles (CIPs)/silicone resin composite with negative thermal expansion filler

Composites with tunable coefficient of thermal expansion (CTE) were prepared by incorporating orthorhombic Pbcn yttrium molybdate (Y₂Mo₃O₁₂) particles at various weight percentages in carbonyl iron particles (CIPs)/silicone resin composite. The porous particles of Y₂Mo₃O₁₂, which has isotropic negative thermal expansion confirmed by high-temperature X-ray powder diffraction, were synthesized using a citric acid method. Results show that porous Pbcn orthorhombic Y₂Mo₃O₁₂ was obtained with α_l = −1.04 × 10⁻⁵ /°C from 100 to 800 °C and the CTE of the CIPs/ silicone resin composite was reduced by around 45 % with the addition of Y₂Mo₃O₁₂ at 20 wt.% loading. The complex permittivity and permeability were investigated in the frequency range of 2.6–18 GHz by wave guide method. Both the real (ε′) and imaginary (ε″) parts of the complex permittivity increase with increasing Y₂Mo₃O₁₂ content, which is ascribed to interfacial interaction between the CIPs and Y₂Mo₃O₁₂. For the permeability, the more dispersed Y₂Mo₃O₁₂ fillers lead to the lower both the real (μ′) and imaginary (μ″) part of permeability due to the dilution effect induced by the addition of Y₂Mo₃O₁₂.