Introduction to Dielectrics

1. 24.4 Dielectrics 24.6 Gauss’s law in dielectrics 24.5 Molecular model of induced charge Introduction to Dielectrics

2. 24.4 Dielectrics d Separate two metal sheet with small gap d Increases the maximum possible potential difference between the capacitor plates Increase the capacitance

3. 24.4 Dielectrics Definition of dielectric constant K Capacitance with dielectrics Capacitance without dielectrics Recall: To store same amount of charge Q, voltage required is reduced for higher K materials Note, K will change respect to temperature and frequency. Also, in a single crystal, K is different along different crystal axes. Strontium titanante (SrTiO3) with K=310 Chromia (Cr2O3) with K=13

4. 24.4 Dielectrics Strontium titanante (SrTiO3) with K=310 Two-dimensional electron gas with universal subbands at the surface of SrTiO3 A. F. Santander-Syro, et al. Nature, 469, 189 (2011) Metallic and Insulating Oxide Interfaces Controlled by Electronic Correlations H. W. Jang, et al. Science, 331, 888 (2011)

5. 24.4 Dielectrics Chromia (Cr2O3) with K=13 Robust isothermal electric control of exchange bias at room temperature Xi He, et al. Nature Materials, 9, 579 (2010) Imaging and Control of Surface Magnetization Domains in a Magnetoelectric Antiferromagnet Ning Wu, et al. Phys. Rev. Lett. , 106, 087272 (2011)

6. 24.4 Dielectrics Recall: and E0 E Also recall: and Definition of the permittivity and

7. 24.4 Dielectrics +Q Example: E1 d/2 K1 E0 V E2 K2 d/2 -Q = =

8. 24.4 Dielectrics High Voltage Ground Cr2O3 Ground Dielectric breakdown or Dielectric strength Air

9. 24.6 Gauss’s Law in Dielectrics Recall: Dielectrics Conductor A A A

10. 24.6 Gauss’s Law in Dielectrics Example: K E1 ra r rb E2

11. 24.5 Molecular Model of induced Charge E E