**4.1.3 Magnetic properties**

114 Polycrystalline Materials – Theoretical and Practical Aspects

In order to analyse the different morphological and surface characteristics of particles in the perovskites, SEM (scanning electron microscopy) can be used. Figure 6 shows a micrograph obtained for La0.75Sr0.25Cr0.2Fe0.8O3 (the figure shows the texture and relief created by the elimination of volatile substances produced in the combustion of organic compounds

In many -but certainly not all- cases new solid compounds are further characterized by a variety of techniques that straddle the fine line that (hardly) separates solid-state chemistry

For non-metallic materials it is often possible to obtain UV/VIS spectra. In the case of semiconductors that will give an idea of the band gap. Surfaces of *AB*O3 perovskites and defects therein are extremely relevant for such important fields of technology as photocatalysis, gas-sensors and for applications as materials for ferroelectric memories, and

Four-point (or five-point) probe methods are often applied either to ingots, crystals or pressed pellets to measure resistivity and the size of the Hall effect. This gives information on whether the compound is an insulator, semiconductor, semimetal or metal and upon the type of doping and the mobility in the delocalized bands (if present). Thus, important

The impedance spectroscopy is also a very useful method used for electrical properties

characterization of perovskite-type materials, especially for bulk ceramic samples.

the optical properties of them can be proved to be extremely interesting.

information is obtained on the chemical bonding in the material.

during thermal treatment).

Fig. 6. SEM for La0.75Sr0.25Cr0.2Fe0.8O3.

**4.1 Further characterization** 

from solid-state physics.

**4.1.1 Optical properties** 

**4.1.2 Electrical properties** 

Magnetic susceptibility can be measured as a function of temperature to establish whether the material is a *para-*, *ferro-*, *ferri-* or *antiferro*- magnet, among others. Again the information obtained pertains to the bonding in the material. This is particularly important for transition metal compounds. In the case of magnetic order neutron diffraction can be used to determine the magnetic structure.

Magnetic measurements are usually carried out with a SQUID magnetometer under different applied magnetic field. Figure 7 shows a picture of one of those SQUID magnetometers.

Fig. 7. SQUID magnetometer.

As an example, Figure 8 shows the magnetic susceptibility versus temperature data for the perovskite Sr2Ru0.5Co1.5O6.

Fig. 8. Magnetic susceptibility versus temperature for Sr2Ru0.5Co1.5O6.

Structural Characterization of New Perovskites 117

destructively (overlapping waves either add together to produce stronger peaks or subtract from each other to some degree), producing a diffraction pattern on a detector or film. The resulting wave interference pattern is the basis of diffraction analysis. This analysis is called

a)

b)

Fig. 9. X-ray powder diffractometer.

Bragg diffraction.
