Accession Number : ADA612442
Title : Poly(aryl-ether-ether-ketone) as a Possible Metalized Film Capacitor Dielectric: Accurate Description of the Band Gap Through Ab Initio Calculation
Descriptive Note : Final rept.
Corporate Author : ARMY RESEARCH LAB ADELPHI MD SENSORS AND ELECTRON DEVICES DIRECTORATE
Personal Author(s) : Ho, Janet ; Olguin, Marco ; Diaz, Carlos
Report Date : Dec 2014
Pagination or Media Count : 22
Abstract : Poly(aryl-ether-ether-ketone) (PEEK) is a primary candidate for a high temperature capacitor dielectric due to its outstanding mechanical strength and thermal stability. However, its breakdown strength is unsatisfactory (400 MV/m) and its volumetric resistivity drops significantly at electric fields above 100 MV/m. Our main objective is to study the effect of chemical impurities, such as water molecules and chain ends, on impurity states in the band gap of PEEK using density functional theory (DFT) to gain insight on the factors impacting electrical resistivity under a high field, which may correlate to low breakdown strength. Our focus is to determine the correct geometry of the unit cell and develop a methodology for computing the band gap of PEEK accurately. We used dispersion-corrected DFT to optimize various starting geometries and determined the correct one based on a comparison with experimental crystallographic data. The band gap was determined from the projected density of states, which is calculated using the HSE06 hybrid exchange-correlation functional. The original HSE06 formulation overestimates the band gap of PEEK by 33% compared to the experimental value. So, to obtain a more accurate functional form, we conducted a systematic study on the parameter space of the functional by varying the exchange-correlation mixing and screening coefficients.
Descriptors : *BAND GAPS , *DENSITY FUNCTIONAL THEORY , *DIELECTRICS , *ELECTRICAL RESISTANCE , HIGH TEMPERATURE , IMPURITIES , KETONES
Subject Categories : Physical Chemistry
Electricity and Magnetism
Quantum Theory and Relativity
Solid State Physics
Distribution Statement : APPROVED FOR PUBLIC RELEASE