tailieunhanh - Electronic Materials Part 8

Tham khảo tài liệu 'electronic materials part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Ionic Polarizability Usually Clausius-Mosotti necessary due to high density of dipoles s r- 1 Na lol s r 2 3S o 1 3s oV a a- 2 e M to I- 201 By convention things are abbreviated by using s and . s. a a_ s r sw -1 sra 2 n 2 1 1 2 7 T la a n 2 3s o V o o Ooi a a s s s 2 s w o 5 o T - 1 a T s 2 w s s 2 E. Fitzgerald-1999 17 Orientational Polarizability No restoring force analogous to conductivity C - p p 0 q -q For a group of many molecules at some temperature Analogous to conductivity the molecules collide after a certain time t giving aDC a . o T 1- iOOT - U pE cose kb T kbT f e e After averaging over the polarization of the ensemble molecules valid for low E-fields p2 a DC 3kbT E. Fitzgerald-1999 18 9 Dielectric Loss For convenience imagine a low density of molecules in the gas phase C-M can be ignored for simplicity There will be only electronic and orientational polarizability . .2 Na DC e r 1 Xe X o n2 DC 3e o 1 - iroT _ .2 Na DC roT 1 e r e so n D 3e o 2 - n2 r n 1 s 1 iroT We can write this in terms of a real and imaginary dielectric constant if we choose r e ie e o n2 1 ro2t 2 1 ro 2t 2 roT Water molecule T 11 sec ffl 1010 microwave oven transmission of E-M waves E. Fitzgerald-1999 19 e n1 n2 e Dielectric Constant vs. Frequency Completely general e due to the localized charge in materials Dispersion-free regions vg vp E. Fitzgerald-1999 20 10 Dispersion Dispersion can be defined a couple of ways same just different way - when the group velocity ceases to be equal to the phase velocity - when the dielectric constant has a frequency dependence . when de dffl not 0 vP ro c ổro v k yỊe r ro dk s E. Fitzgerald-1999 21 .