We present the results of two multi-wavelength studies of the angular diameters of the Mira-like stars ο Cet, W Hya and R Leo. The MAPPIT experiment was able to deliver diameters of these stars over a continuous wavelength region from 0.65 – 1 micron, while the Keck aperture-masking experiment was able to deliver diameters between 1.2 and 3.5 microns. Strong size variations with wavelength were recorded for all stars, and we discuss the implications for model atmospheres of these stars, and speculate on the necessity of including dust scattering in radiative transfer calculations.

Solid solution series of the type K2Bi8-xSbxSe13, K2-xRbxBi8Se13 as well as K2Bi8Se13-xSx were prepared and the distribution of the atoms (Bi/Sb, K/Rb and Se/S) on different crystallographic sites, the band gaps and their thermoelectric properties were studied. The distribution Se/S appears to be more uniform than the distribution of the Sb and Rb atoms in the β-K2Bi8Se13 structure that shows preference in specific sites in the lattice. Band gap is mainly affected by Sb and S substitution. Seebeck coefficient measurements showed n-type character for of all Se/S members. In the Bi/Sb series an enhancement of p-type character was observed. The thermoelectric performance as well as preliminary high temperature measurements suggest the potential of these materials for high temperature applications.

A new series of low-melting, highly volatile, thermally and air-stable cadmium MOCVD precursors have been synthesized and characterized. Cd(hfa)2(N, N-DE-N', N'-DMEDA) has been successfully utilized in the growth of highly conductive and transparent CdO thin films. Hall measurements conducted on films deposited simultaneously on MgO (100) single crystal and Corning 1737F glass substrates reveal that the films on MgO have significantly enhanced carrier mobilities. Owing to similar grain sizes and carrier concentrations we attribute this effect to improved texture and associated improvements crystalline order. Conductivities as high as 8,590 S/cm are obtained which is to our knowledge the highest value reported to date for CdO films without aliovalent dopants.

In previous studies we have investigated the thermoelectric properties of undoped and doped compositions of β-K2Bi8Se13. The attempt to substitute Rb for K resulted in a different structure type, but with potentially useful thermal properties. In this paper the results of measuring the thermoelectric properties of small crystalline samples for K2−xRbxBi8Se13 solid solutions are reported for the compositional ranges with 0 ≤ × ≤ 1 and with 1.8 ≤ × ≤ 2. The presence of rubidium provides a significant improvement in the thermopower but has much less of an effect on the electrical conductivity. The combined results are reflected in the power factor behavior as a function of temperature.

We have previously reported the successful p-type doping of CsBi4Te6 which had a high figure of merit at temperatures below 300 K. In this study, several dopants were explored to make n-type CsBi4Te6. A program of measurements was performed to identify the optimum doping concentration for several series of dopants. The highest power factors occurred around 125 K for the 0.5% Sn doped CsBi4Te6 sample which had a power factor of 21.9 μW/cm•K2 and 1.0% Te doped CsBi4Te6 which had a power factor of 21.7 μW/cm•K2.

Based on the versatile combination of PbQ- and Bi2Q3-type (Q = S, Se, Te) fragments, we explored new compounds in the Pb/Bi/Se ternary system. The new class of compounds, Pb5Bi6Se14, Pb5Pb12Se23, and PbBi8Se13 are homologues with different combination of alternating Bi2Se3- and PbSe-type layers. α- and β-Pb6Bi2Se9 were obtained in different synthetic conditions and the former is isostructural to heyrovskyite (Pb6Bi2S9) while the latter is a NaCl-type cubic phase. Pb5Bi6Se14 shows a power factor of 11.2 μW/cm·K2 with electrical conductivity of 657 S/cm and thermopower of -131 μV/K at 271 K. The most significant characteristic of this material is the extremely low thermal conductivity of less than 1.0 W/m·K at room temperature. On the basis of these properties, a preliminary doping study for Pb5Bi6Se14 with Sn, Sb, and SbBr3 as dopants was undertaken and the results are presented in this report.

The synthesis, physicochemical, spectroscopic, and structural characterization of the compound β-K2Bi8Se13 has been previously reported. The results indicated that this material should be investigated further for possible thermoelectric applications. β-K2Bi8Se13 exhibits excellent electrical conductivity values at room temperature while maintaining high Seebeck coefficients. In this work, the optimization of the compound β-K2Bi8Se13 is continued by the introduction of varying concentrations of several different dopants. The value of x in K2Bi8– xSbxSe13 was varied in order to find the composition with minimum thermal conductivity. Where possible, transport measurements were carried out on both single crystal and polycrystalline ingot material. From these data, the trends in the key parameters were identified for optimizing the power factor and figure of merit.

We present the structure and thermoelectric properties of the new quaternary selenides K1+xM4–2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22. The compounds K1+xM4-2xBi7+xSe15 (M= Sn, Pb) crystallize isostructural to A1+xPb4-2xSb7+xSe15 with A = K, Rb, while K1-xSn5-xBi11+xSe22 reveals a new structure type. In both structure types fragments of the Bi2Te3-type and the NaCl-type are connected to a three-dimensional anionic framework with K+ ions filled tunnels. The two structures vary by the size of the NaCl-type rods and are closely related to β-K2Bi8Se13 and K2.5Bi8.5Se14. The thermoelectric properties of K1+xM4-2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22 were explored on single crystal and ingot samples. These compounds are narrow gap semiconductors and show n-type behavior with moderate Seebeck coefficients. They have very low thermal conductivity due to an extensive disorder of the metal atoms and possible “rattling” K+ ions.

Amorphous silicate grains known as GEMS have been found in chondritic porous interplanetary dust particles (IDPs) from comets. GEMS are composed of nanometer-sized FeNi metal and Fe-rich sulfide crystals embedded in silicate glass. The properties of GEMS appear to have been shaped primarily by exposure to ionizing radiation and, since the irradiation occurred prior to accretion of the cometary IDPs, GEMS may have formed either in the solar nebula or presolar interstellar environments. The sizes, shapes, structures, and compositions of GEMS correspond to those of interstellar “amorphous silicate” grains. Nanometer-sized superparamagnetic metal inclusions dispersed throughout GEMS provide a logical explanation for alignment of interstellar silicate grains in the galactic magnetic field. Irrespective of their origins, GEMS are an important class of submicrometersized chondritic objects. If they were formed in the solar nebula, then they are among the oldest known solar nebula solids. If they are presolar, then they are probably examples of the “amorphous silicate” grains which are ubiquitous throughout the interstellar medium.