Infrared studies of textured ceramic high-Tc superconductors

The surfaces of ceramic samples of high-temperature superconductors can have a high degree of crystalline orientation, depending of the way in which they are prepared. (In particular it is essential that the sample not be polished in an attempt to “improve” the optical quality.) The surfaces of these textured ceramic samples consist of small crystallites, with about 80% orientation of the crystallographic c axis normal to the surface. The infrared and optical properties of these samples have been measured. We observe that the frequency-dependent conductivity can be decomposed into the sum of a far-infrared Drude part (which at zero frequency equals the ordinary dc conductivity) and a broad, temperature-independent mid-infrared band. The mid-infrared band has about four times the oscillator strength of the low-frequency Drude part.