S. P. Lebedev

Dielectric measurements in the submillimeter wavelength region

Abstract The paper describes a method for dielectric measurements in the submillimeter range based on the application of a backward-wave-oscillator technique. The application of submillimeter dielectric spectroscopy for solving real problems of solid-state physics is discussed.

Proton modes in the crystals of KH2PO4 family

Abstract According to the present conceptions, excitation of the proton subsystem is of principle importance for the dynamics of phase tran- sitions of the KH2P04 type crystals and, therefore, it is an object of thorough experimental investigation. The present paper is concerned with the investigation of proton modes by means of dielectric spectroscopy in submillimetre wave range, Just in this spectrum range lies the region of fundamental ferroelectric dispersion of the KH2p04 family crystals.

Dielectric dispersion of KH2PO4 and Pb5Ge3O11 crystals at frequencies of 6–12 cm−1

Abstract The dependences of real and imaginary parts of dielectric functions of KH2PO4 and Pb5Ge3O11 vs. temperature and frequency have been obtained in the submillimeter region above as well as below Tc . The results have been compared with the widely adopted phenomenological models and their parameters have been calculated. It is of particular interest that our data for KH2PO4 in paraelectric phase were described by the Debye relaxation model quite exactly. The data for Pb5Ge3O11 in both phases were well represented by the overdamped oscillator function.

Submillimeter dielectric spectra of SC(NH2)2 and BaMnF4 single crystals

The dielectric spectra of thiourea and BaMnF4 were determined in all phases (85-300 K) in the 3-30 cm-1 region using the monochromatic spectrometer with tunable oscillator. Moreover, far infrared (30-450 cm-1) reflectivity of BaMnF4 at 90 and 300 K was measured and evaluated to obtain the dielectric spectra. In the case of thiourea a new extra mode near 7 cm-1 was observed in the paraelectric region. A rather complex dielectric dispersion was found in incommensurate phases in qualitative accord with theoretical expectations. In the case of BaMnF4, two low-frequency modes which partially soften at Tc were found in agreement with recent Raman results.

Relaxation mode in dielectric spectra of CsH2PO4

Abstract The paper presents the results of dielectric investigations and the study of the soft relaxation mode at the paraelectric phase of CsH2PO4 crystal in the frequency region between 10 and 400 GHz.

Subterahertz BWO spectroscopy: methods and devices

Modern sub-terahertz (subTHz) spectrometers, based on coherent sources of radiation, the backward-wave oscillators (BWOs), are described which cover the frequencies V=1 cm/sup -1/-48 cm/sup -1/ (30-1450 GHz) and allow for measurements at temperatures 2-1000 K, also in magnetic fields. They allow for direct determination of spectra of any optical parameter of a material at millimeter-submillimeter wavelengths, the domain where infrared or microwave spectrometers encounter serious methodological difficulties. We report on new technical abilities of the quasioptical BWO-spectrometers and discuss their main components.

Ferroelectric dynamics of ortho-phosphate crystals

Abstract The present paper is concerned with the theoretical and experimental investigations of dynamic properties of ferroactive subsystems of ortho-phosphate crystals.