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Abstract Semiconducting polymers are of interest due to their solution processibility and broad electronic applications. Electrochemistry allows these wide bandgap semiconductors to be converted to conducting polymers by doping such polymers at various potentials. When polymers arep‐doped to improve their conductivity via electrochemical oxidation, various positively‐charged carriers are created, including polarons (singly‐charged) and bipolarons (doubly‐charged). Carrier creation is accompanied by anion intercalation from the electrolyte for charge balance, and this insertion requires ion mobility. In this work, poly(3‐hexylthiophene) (P3HT) with different regioregularities is used to understand the relationship between solvent swelling, which affects anion intercalation, and electrochemical doping. Cyclic voltammetry, optical absorption spectroscopy, and grazing incidence wide‐angle X‐ray scattering (GIWAXS) measurements are used to correlate the doping level with structural changes. In situ electrochemical quartz crystal microbalance (EQCM) measurements are used to quantify the swelling of the polymers dynamically during electrochemical cycling. Lastly, in situ conductivity measurements are done to measure the effect of swelling on the ionic and electronic conductivity. The results indicate that solvent swelling is required for bipolaron formation, and that swelling facilitates both the small structural changes need for polaron formation and the disordering required for bipolaron formation. 

Non-hydrostatic high pressure X-ray diffraction is used to study the hardness of superhard ReB₂nanocrystals. All nanocrystals show less plastic deformation under load than bulk ReB₂, with the smallest nanocrystals showing the most enhancement. 

Alloys of tungsten tetraboride (WB4) with the addition of C and Si were prepared by arc-melting of the constituent elements. The phase purity was established by powder X-ray diffraction (PXRD) and surface morphology by scanning electron microscopy (SEM) analysis. Vickers hardness measurements showed hardness enhancement for alloys with a nominal composition of (W0.98Si0.02):11.6B and (W0.95C0.05):11.6B of 52.2 ± 3.0 and 50.5 ± 2.5 GPa, respectively, compared to 41.2 ± 1.4 GPa for pure WB4. (W0.92Zr0.08):11.6B was determined in previous work to have a hardness of 55.9 ± 2.8 GPa. Bulk moduli were calculated following analysis of high-pressure radial diffraction data and were determined to be 329 ± 4 (K0′ = 2) and 390 ± 9 (K0′ = 0.6) GPa for 8 atom % Zr and 5 atom % C-doping, respectively, compared to 326–339 GPa for pure WB4. Computational analysis was used to determine the dopant positions in the crystal structure, and it was found that Zr primarily substitutes W in the 2c position, Si substitutes for the entire B3 trimers, and C inserts in the Bhex-layer. The hardness enhancement in the case of Zr-doping is attributed primarily to extrinsic hardness effects (nanograin morphology), in the case of C─to intrinsic effects (interlayer bond strengthening), and in the intermediate case of Si─to both intrinsic and extrinsic effects (bond strengthening and fine surface morphology).