[en] The spectra of far-infrared transmission in Tb₃Fe₅O₁₂ magnetoelectric single crystals have been studied in the range between 15 and 100 cm^-1, in magnetic fields up to 10 T, and for temperatures between 5 and 150 K. We attribute some of the observed infrared-active excitations to electric dipole transitions between ligand-field split states of Tb³⁺ ions. Anticrossing between the magnetic exchange excitation and the ligand-field transition occurs at the temperature between 60 and 80 K. The corresponding coupling energy for this interaction is 6 cm^-1. Temperature-induced softening of the hybrid IR excitation correlates with the increase in the static dielectric constant. We discuss the possibility for hybrid excitations of magnons and ligand-field states and their possible connection to the magnetoelectric effect in Tb₃Fe₅O₁₂.

[en] Radon calibration chamber has been constructed to test and calibrate radon and radon progeny detectors at various environmental conditions and to study the characteristic behavior of radon decay products. The size of main room in the chamber is 3.2 mx3.3 mx2.4 m (25.3 m³) and the total volume of the chamber is 39.1 m³. The maximum concentration of radon in the chamber can be maintained up to 250 kBq m^-3 and temperature and humidity are controlled in the ranges of (10-40) deg. C and (30-80)%, respectively. The equilibrium factor and unattached fraction of radon progeny are determined at the radon concentration of 2 kBq m^-3

[en] The effect of Fe doping (<20%) on the Mn site in the ferromagnetic (x=0.37) and the antiferromagnetic (x=0.53) phases of La_1-xCa_xMnO₃ has been studied. Upon doping, no appreciable structure changes have been found in either series. However, conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. These results are not due to the strong lattice effects commonly seen in doping of the La sites. Rather, replacement of Mn³⁺ by Fe³⁺ depopulates the hopping electrons, and weakens the double exchange. The effect of Fe doping can be explained in terms of the band structure. copyright 1997 American Institute of Physics

[en] Growth characteristics of silica particles have been studied experimentally using in situ particle sampling technique from H₂/O₂/Tetraethylorthosilicate (TEOS) diffusion flame with carefully devised sampling probe. The particle morphology and the size comparisons are made between the particles sampled by the local thermophoretic method from the inside of the flame and by the electrostatic collector sampling method after the dilution sampling probe. The Transmission Electron Microscope (TEM) image processed data of these two sampling techniques are compared with Scanning Mobility Particle Sizer (SMPS) measurement. TEM image analysis of two sampling methods showed a good agreement with SMPS measurement. The effects of flame conditions and TEOS flow rates on silica particle size distributions are also investigated using the new particle dilution sampling probe. It is found that the particle size distribution characteristics and morphology are mostly governed by the coagulation process and sintering process in the flame. As the flame temperature increases, the effect of coalescence or sintering becomes an important particle growth mechanism which reduces the coagulation process. However, if the flame temperature is not high enough to sinter the aggregated particles then the coagulation process is a dominant particle growth mechanism. In a certain flame condition a secondary particle formation is observed which results in a bimodal particle size distribution

[en] High-pressure resistivity and X-ray diffraction measurements were conducted on La_0.85MnO_3-δ at ∼6 and ∼7 GPa, respectively. At low pressures the metal-insulator transition temperature (T_MI) increases linearly up to a critical pressure, P^* ∼3.4 GPa, followed by reduction in T_MI at higher pressure. Analysis of the bond distances and bond angles reveals that a bandwidth increase drives the increase in T_MI below P^*. The reduction in T_MI at higher pressures is found to result from Jahn-Teller distortions of the MnO₆ octahedra. The role of anharmonic interatomic potentials is discussed.