TY - JOUR
T1 - TEM characterization of modulated microstructures in CaO-Dy2O3 solid solutions
AU - Kim, Y. J.
AU - Kriven, W. M.
N1 - Funding Information:
This work was supportedb y a grant from the Departmenot f Energy (DE-AC02-76ER 01198) throught he MaterialsR esearchL aboratoryo f the Universityo f Illinois at Urbana-ChampaigTnh. e
PY - 1991/8
Y1 - 1991/8
N2 - The lanthanide sesquioxides (e.g. Dy2O3) have been identified as potential high-temperature transformation tougheners alternative to zirconia (ZrO2). The monoclinic (B) to cubic (C) transformation on cooling is accompanied by an 8% volume increase and shattering. In the course of work to stabilize the B phase by adding CaO to pure Dy2O3 and rapid cooling, modulated microstructures were found in B phases of CaO-Dy2O3 solid solutions. Primarily two unit-cell scale modulations were identified: q1 (001-type, λ ≈ 9.0 Å) and q2 (200-type, λ ≈ 7.5 Å). In the [010] orientation another modulatio n (q3; λ ≈ 40 Å) occured in some samples. Higher-order satellite reflections of q1 and q2 were always present and their intensities gradually decreased as the order increased. However, q3 showed strong first-order intensities but weak higher-order intensities. As the cooling rate increased, angles q1<(00-)* and q2<(600)* tended to increase, whereas the intensity of q3 tended to decrease or diffuse. As the sintering temperature and time increased, the intensity of q3 tended to increase. A structural model to explain the modulated structures was proposed. It was suggested that the origin of the q1 and q2 modulations was a crystallographic shearing of structural units. The systematic shearing locally generated domains similar to the C structure, which gave rise to the q3 modulation.
AB - The lanthanide sesquioxides (e.g. Dy2O3) have been identified as potential high-temperature transformation tougheners alternative to zirconia (ZrO2). The monoclinic (B) to cubic (C) transformation on cooling is accompanied by an 8% volume increase and shattering. In the course of work to stabilize the B phase by adding CaO to pure Dy2O3 and rapid cooling, modulated microstructures were found in B phases of CaO-Dy2O3 solid solutions. Primarily two unit-cell scale modulations were identified: q1 (001-type, λ ≈ 9.0 Å) and q2 (200-type, λ ≈ 7.5 Å). In the [010] orientation another modulatio n (q3; λ ≈ 40 Å) occured in some samples. Higher-order satellite reflections of q1 and q2 were always present and their intensities gradually decreased as the order increased. However, q3 showed strong first-order intensities but weak higher-order intensities. As the cooling rate increased, angles q1<(00-)* and q2<(600)* tended to increase, whereas the intensity of q3 tended to decrease or diffuse. As the sintering temperature and time increased, the intensity of q3 tended to increase. A structural model to explain the modulated structures was proposed. It was suggested that the origin of the q1 and q2 modulations was a crystallographic shearing of structural units. The systematic shearing locally generated domains similar to the C structure, which gave rise to the q3 modulation.
UR - http://www.scopus.com/inward/record.url?scp=0026206350&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0026206350&partnerID=8YFLogxK
U2 - 10.1016/0304-3991(91)90032-2
DO - 10.1016/0304-3991(91)90032-2
M3 - Article
AN - SCOPUS:0026206350
SN - 0304-3991
VL - 37
SP - 351
EP - 361
JO - Ultramicroscopy
JF - Ultramicroscopy
IS - 1-4
ER -