The thermal properties were investigated for hot‐pressed zirconium diboride—transition‐metal boride solid solutions. The transition‐metal additives included hafnium, niobium, tungsten, titanium, and yttrium. The nominal additions were equivalent to 3 at.% of each metal with respect to zirconium. Powders were hot‐pressed to nearly full density at 2150°C using 0.5 wt% carbon as a sintering aid. Thermal diffusivity was measured using the laser flash method. Thermal conductivity was calculated from the thermal diffusivity results using temperature‐dependent values for density and heat capacity. At 25°C, the thermal conductivity ranged from 88 to 34 W·(m·K)−1 for specimens with various additives. Electrical resistivity measurements and the Wiedemann–Franz law were used to calculate the electron contribution of the thermal conductivity and revealed that thermal conductivity was dominated by the electron contribution. The decrease in thermal conductivity correlated with a decrease in unit cell volume, indicating that lattice strain may affect both phonon and electron transport in ZrB2.

Infrared (IR) glass-ceramics (GCs) hold the potential to dramatically expand the range of optical material solutions available for use in bulk and planar optical systems in the IR. Current material solutions are limited to single-or polycrystalline materials and traditional IR-transparent optical glasses. GCs that can be processed with spatial control and extent of induced crystallization present the opportunity to realize an effective refractive index variation, enabling arbitrary gradient refractive index elements with tailored optical function. This work discusses the role of the parent glass composition and morphology on nanocrystal phase formation in a multicomponent chalcogenide glass. Through a two-step heat treatment protocol, a Ge-As-Pb-Se glass is converted to an optical nanocomposite where the type, volume fraction, and refractive index of the precipitated crystalline phase(s) define the resulting nanocomposite's optical properties. This modification results in a giant variation in infrared Abbe number, the magnitude of which can be tuned with control of crystal phase formation. The impact of these attributes on the GCs' refractive index, transmission, dispersion, and thermo-optic coefficient is discussed. A systematic protocol for engineering homogeneous or gradient changes in optical function is presented and validated through experimental demonstration employing this understanding.

The effect of Hf additions on the thermal properties of ZrB 2 ceramics was studied. Reactive hot pressing of ZrH 2 , B, and HfB 2 powders was used to synthesize (Zr 1 -x ,Hf x )B 2 ceramics with Hf contents ranging from x = 0.0001 (0.01 at.%) to 0.0033 (0.33 at.%). Room-temperature heat capacity values decreased from 495 JÁ(kgÁK)-1 for a Hf content of 0.01 at.% to 423 JÁ(kgÁK)-1 for a Hf content of 0.28 at.%. Thermal conductivity values decreased from 141 to 100 WÁ(mÁK) -1 as Hf content increased from 0.01 to 0.33 at.%. This study revealed, for the first time, that small Hf contents decreased the thermal conductivity of ZrB 2 ceramics. Furthermore, the results indicated that reported thermal properties of ZrB 2 ceramics are affected by the presence of impurities and do not represent intrinsic behavior.

The thermal properties were investigated for hot‐pressed zirconium diboride containing solid solution additions of tantalum, molybdenum, rhenium, vanadium, and chromium. The nominal additions were equivalent to 3 at.% of each metal with respect to zirconium. Using 0.5 wt% carbon as a sintering aid, powders were hot‐pressed to near full density at 2150°C. Rietveld refinement of X‐ray diffraction data was used to measure lattice parameters and to ensure that the additives formed solid solutions. Thermal conductivities were calculated from measured thermal diffusivities and temperature‐dependent values for density and heat capacity. Thermal conductivities at 25°C ranged from 88 W·(m·K)−1 for nominally pure ZrB2 down to 28 W·(m·K)−1 for (Zr,Cr)B2. Electron contributions to thermal conductivity were calculated from electrical resistivity measurements using the Wiedemann–Franz law. Decreases in phonon and electron conduction correlated with the size of the metallic additive, indicating that changes in atom size in the Zr lattice positions reduced thermal transport.

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