Fred Dynys

High temperature properties of BiScO3–PbTiO3 piezoelectric ceramics

Smart actuators and intelligent structures are sought after for aeronautical applications. As a result of high Curie temperature (430 °C) and piezoelectric coefficient (>200 pC/N), BiScO3–PbTiO3 (BS-PT) ceramics are prospective materials for high temperature actuators. This paper reports on the temperature dependent electrical, ferroelectric, and electromechanical properties of liquid phase sintered BS-PT ceramics. Compared to solid state sintered BS-PT, liquid phase sintered BS-PT with Bi2O3 showed improved electrical performance: (1) threefold reduction in loss tangent at elevated temperatures, (2) fivefold increase in dc resistivity at high electrical fields, and (3) 15% increase in high field piezoelectric coefficient. Hysteresis loops of the highly resistive ceramics were saturated and showed no major dependence on the magnitude and the frequency of the applied field. BS-PT ceramics exhibit depoling behavior at temperatures below (>350 °C) the Curie temperature (430 °C). Liquid phase sintering using ...

Thermoelectric properties of CoxNi4-xSb12-ySnyTernary Skutterudites

Jon A. Mackey Mechanical Engineering, University of Akron, Akron, Ohio, 44325 Frederick W. Dynys NASA Glenn Research Center, Cleveland, Ohio, 44135 and Alp Sehirlioglu Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio, 44106 Thermoelectric materials based on the skutterudite crystal structure have demonstrated enhanced performance (ZT>1), along with good thermal stability and favorable mechanical properties. Binary skutterudites, with single and multiple fillers, have been intensively studied in recent years. Compared to binary skutterudites, the ternary systems have received less attention, e.g. Ni4Sb8Sn4. Ternary skutterudites are isoelectronic variants of binary skutterudites; cation substitutions appear to be isostructural to their binary analogues. In general, ternary skutterudites exhibit lower thermal conductivity. Ternary systems of Ni4Bi8Ge4, Ni4Sb8Ge4, and Ni4Sb8Sn4 were investigated using combined solidification and sintering steps. Skutterudite formation was not achieved in the Ni4Bi8Ge4 and Ni4Sb8Ge4 systems; skutterudite formation occurred in Ni4Sb8Sn4 system. P-type material was achieved by Co substitution for Ni. Thermoelectric properties were measured from 298 K to 673 K for Ni4Sb8Sn4, Ni4Sb7Sn5 and Co2Ni2Sb7Sn5. N-type Ni4Sb8Sn4 exhibit the highest figure of merit of 0.1 at 523 K.