| The perovskite layer structure (PLS) compounds have the general formula (A{dollar}sp{lcub}2+{rcub})sb2{dollar}(B{dollar}sp{lcub}5+{rcub})sb2{dollar}O{dollar}sb7{dollar}, or (A{dollar}sp{lcub}3+{rcub})sb2{dollar}(B{dollar}sp{lcub}4+{rcub})sb2{dollar}O{dollar}sb7{dollar}, and crystallize in a very anisotropic layered structure consisting of parallel slabs made up of perovskite units.; Several of these compounds possess the highest Curie temperatures (T{dollar}sb{lcub}rm c{rcub}{dollar}) of any known ferroelectrics. Two examples are Sr{dollar}sb2{dollar}Nb{dollar}sb2{dollar}O{dollar}sb7{dollar} with T{dollar}sb{lcub}rm c{rcub}{dollar} of 1342{dollar}spcirc{dollar}C, and La{dollar}sb2{dollar}Ti{dollar}sb2{dollar}O{dollar}sb7{dollar} with T{dollar}sb{lcub}rm c{rcub}{dollar} of 1500{dollar}spcirc{dollar}C. This thesis is an investigation of PLS ceramics and their feasibility as a high temperature transducer material. Piezoelectricity in single crystals has been measured, but the containerless float zone apparatus necessary to grow high quality crystals of these refractory compounds is expensive and limited to a small number of research groups. Previous attempts to pole polycrystalline Sr{dollar}sb2{dollar}Nb{dollar}sb2{dollar}O{dollar}sb7{dollar} have failed, and to this point piezoelectricity has been absent. The initiative taken in this research was to investigate PLS ceramics by way of composition and processing schemes such that polycrystalline bodies could be electrically poled. The ultimate objective then was to demonstrate piezoelectricity in PLS ceramics, especially at high temperatures.; Donor-doping of both La{dollar}sb2{dollar}Ti{dollar}sb2{dollar}O{dollar}sb7{dollar} and Sr{dollar}sb2{dollar}Nb{dollar}sb2{dollar}O{dollar}sb7{dollar} was found to increase volume resistivities at elevated temperatures, an important parameter to consider during the poling process. Sr{dollar}sb2{dollar}Ta{dollar}sb2{dollar}O{dollar}sb7{dollar} (T{dollar}sb{lcub}rm c{rcub}{dollar} = {dollar}-{dollar}107{dollar}spcirc{dollar}C) was used to make solid solution compositions with moderately high Curie temperatures, of about 850{dollar}spcirc{dollar}C, and lower coercive fields.; A hot-forging technique was employed to produce ceramics with high density ({dollar}>{dollar}99% of theoretical) and high degree of grain orientation ({dollar}>{dollar}90%). Texturing was characterized by x-ray diffraction and microscopy. Considerable anisotropy was observed in physical and electrical properties, including thermal expansion, resistivity, dielectric constant, and polarization. The direction perpendicular to the forging axis proved to be the ferroelectric "easy" direction, indicating that the polar axis lies in the plane of the plate-like grains.; Hot-forged samples were poled at 40 to 50 KV/cm at 200{dollar}spcirc{dollar}C. Several compounds in the La{dollar}sb2{dollar}Ti{dollar}sb2{dollar}O{dollar}sb7{dollar}-Sr{dollar}sb2{dollar}Nb{dollar}sb2{dollar}O{dollar}sb7{dollar}-Sr{dollar}sb2{dollar}Ta{dollar}sb2{dollar}O{dollar}sb7{dollar} ternary system were shown to be piezoelectric. From appropriately oriented cuts, the dielectric, elastic, and piezoelectric coefficients were determined by the resonance method. Relative to commercial piezoelectric ceramics such as Pb(ZrTi)O{dollar}sb3{dollar}, hot-forged PLS ceramics were found to have high frequency constants, low compliance, low electromechanical coupling, low piezoelectric coefficients, and high mechanical quality factors. For Sr{dollar}sb2{dollar}(Nb{dollar}sb{lcub}0.5{rcub}{dollar}Ta{dollar}sb{lcub}0.5{rcub})sb2{dollar}O{dollar}sb7{dollar}, N{dollar}sb{lcub}32{rcub}{dollar} = 2216 Hz-m, s{dollar}sb{lcub}32{rcub}{dollar} = 8.37 {dollar}times{dollar} 10{dollar}sp{lcub}-12{rcub}{dollar} m{dollar}sp2{dollar}/N, k{dollar}sb{lcub}32{rcub}{dollar} = 3.60%, d{dollar}sb{lcub}32{rcub}{dollar} = 2.40 pC/N, and Q{dollar}sb{lcub}rm m{rcub}{dollar}... |
