This paper reviews the recent developments of spectroscopy techniques as well as the recent observations of new types of soft modes. Instrumentations for measurements of infrared reflectivity, Raman scattering, hyper-Raman scattering and Brillouin scattering are summarized. The new type phase transitions, such as ferroelastic, staggered and incommensurate phase transitions are introduced. Finally future problems on softmode spectroscopy are discussed.
The interference contrast microscope reveals unit-cell and/or sub-unit-cell step structures. Such micro-steps are often found on faces of as-grown crystals prepared with a chemical vapour deposition method. Referring to FeCr2S4, CdCr2Se4 and Cr2S3, examples of growth patterns with step height from 5.8 to 17.2A were presented. Often steps originated from partial screw dislocations were observed. With respect to Cr2S3, the steps half unit-cell high coagulated into unit-cell steps accompanied with characteristic interlacing half unit-cell steps. Due to the instablility of the piled atomic layers to a height of a unit-cell at steps, they often decompose with the creation of interlaced step structures. Two interlaced steps coagulate and annihilate when they meet.