Engineering topics

Kim, Q.

Publications and source records attributed to Kim, Q..

39 records · Page 3

NASA NTRS1984

Discoloration of poly(vinyl butyral) in cells exposed to real and simulated solar environments

The discoloration of poly(vinl butyral) (PVB) films used in solar cell modules is described. Transmission absorption, Fourier transformation IR absorption and atomic absorption spectroscopy as well as scanning electron microscopy were used for this study. The discoloration of the PVB has been found to be affected by oxygen, moisture, temperature and light. However, the most severe discoloration observed is clearly associated with the migration of positive silver ions, which can be accelerated in the presence of electric fields. The metallization is the source of the silver, and the data are consistent with an interfacial reaction between the silver and PVB followed by transport into the polymer.

Kim, Q.↗

NASA NTRS1983

Low frequency dielectric relaxation in boracites

In order to elucidate the nature of the imperfections which adversely affect pyroelectric processes in boracites, the thermal and dispersive characteristics of the low frequency dielectric response in iron-iodide boracite (Fe3B7O13I) and copper-chloride boracite (Cu3B7O13Cl) have been investigated. These characteristics were measured as a function of crystallographic orientation and applied field in both the ferroelectric and paraelectric states. The low frequency dielectric relaxation of 100 line oriented multi-domain copper-chloride boracite clearly indicates the dipole nature of the lattice imperfections. The activation energies calculated from a noninteracting Debye model, are 0.53 eV in the ferroelectric phase and 0.10 eV in the paraelectric phase.

Kim, Q.↗

NASA NTRS1981

Raman study of the improper ferroelectric phase transition in iron iodine boracite

The reduction in the dielectric anomaly near the phase transition temperature in improper ferroelectrics suggests that this behavior may be exploited to significantly enhance the figure-of-merit for pyroelectric infrared detection. This reduction is associated with a decoupling of the thermal and dielectric responses which, in turn, reflects the unusual nature of the lattice instability at the phase transition. In order to elucidate the characteristics of the phonon behavior connected with the lattice instability, Raman scattering of Fe3B7O13I has been examined in both the paraelectric and ferroelectric phases. The results of this study as well as results from earlier measurements on other boracites, provides insight into the nature of the mode softening.

Kim, Q.↗