Negative entropy of mixing for vanadium-platinum solutions

Exploring Pore Formation and Gas Sensing Kinetics Using Conjugated Polymer-Small Molecule Blends

Controlling miscibility between mixture components helps induce spontaneous phase separation into distinct domain sizes, thereby resulting in porous conjugated polymer (CP) films with different pore sizes after selective removal of auxiliary components. The miscibility of the CP mixture can be tailored by blending auxiliary model components designed by reflecting the difference in solubility parameters with the CP. The pore size increases as the difference in solubility parameters between the matrix CP and auxiliary component increases. Electrical properties are not critically damaged even after forming pores in the CP; however, excessive pore formation enables pores to spread to the vicinity of the dielectric layer of CP-based field-effect transistors (FETs), leading to partial loss of the carrier-transporting active channel in the FET. The porous structure is advantageous for not only increasing detection sensitivity but also improving the detection speed when porous CP films are applied to FET-based gas sensors for NO2 detection. The quantitative analysis of the response-recovery trend of the FET sensor using the Langmuir isotherm suggests that the response speed can be improved by more than 2.5 times with a 50-fold increase in NO2 sensitivity compared with pristine CP, which has no pores.

Charge redistribution and phonon entropy of vanadium alloys

The effects of alloying on the lattice dynamics of vanadium were investigated using inelastic neutron scattering. Phonon densities of states were obtained for bcc solid solutions of V with 3d, 4d, and 5d transition metal solutes, from which vibrational entropies of alloying were obtained. A good correlation is found between the vibrational entropy of alloying and the electronegativity of transition metal solutes across the 3d row and down columns of the periodic table. First-principles calculations on supercells matching the experimental compositions predicted a systematic charge redistribution in the nearest-neighbor shell around the solute atoms, also following the Pauling and Watson electronegativity scales. The systematic stiffening of the phonons is interpreted in terms of the modified screening properties of the electron density around the solutes.