Optical and X-Ray Single Crystal Studies of the Monoclinic ⇌ Tetragonal Transition in ZrO2 |
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Authors: | S T BULJAN H A McKINSTRY V S STUBICAN |
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Affiliation: | Materials Research Laboratory and Materials Sciences Department, The Pennsylvania State University, University Park, Pennsylvania 16802 |
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Abstract: | The monoclinic ? tetragonal phase transition in ZrO2 single crystals was studied at temperature by transmission optical microscopy and X-ray diffraction techniques. A series of timelapse photographs illustrated the relations between the events that occur during the transition. The events themselves were recognized by direct observation using a high-temperature microscope stage and by scrutiny of several high-temperature Laue photographs. During heating the monoclinic phase transforms to the tetragonal by the motion of an interface parallel to the (100) m plane; simultaneous twinning also occurs behind the advancing interface. The tetragonal phase is usually twinned on the (1 2) bct or ( 12) bct plane, and the extent of twinning is influenced by the heating rate. Cooling transforms the untwinned tetragonal form into a twinned monoclinic form with the orientation of the monoclinic twins parallel to the trace of the (001) m plane when observations are made in the (100) m plane. Transformation of a twinned tetragonal crystal results in twins on the {110} m and {001} m planes. Orientation relations in the ZrO2 transformation are: (100) m ‖(110) bct , 010] m ‖001] bct , and by the virtue of twinning, (100) m ‖(110) bct , 001] m ‖001] bct . During cooling the same topotaxial relations are maintained. |
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