(a) Schematic depicting the X17-B1 beamline at NSLS-BNL and the diffraction stage used for ultra-high energy energy dispersive x-ray diffractometry using a polychromatic synchrotron probe comprised of 200 keV photons. Here, the gauge volume is stationary in space and placed on the body center of the specimen. The depicted method is a transmission (Laue) method. Gauge volume controlled by incident slit opening and gauge length. Gauge length controlled by Bragg angle which is fixed in this method. Due to highly penetrating nature of the x-rays used, specimen is measured in situ while an electric field is imposed on it and heated concomitantly, (b) Schematic depicting the custom hot-stage used in the current experiment. The specimen and the Ohmic contacts are sandwiched between two spring-loaded insulator plates. The insulator plates are wrapped with a heating coil. The thermocouple is placed in the immediate vicinity of the specimen. The specimen is surrounded with high temperature “wool” for thermal insulation (not shown).
Schematic summarizing the current-time history of 8% Y2O3-ZrO2 during the in situ experiment. The duration of the 876–905 °C temperature range corresponds to 199 s over which densification has taken place. Maximum current draw permitted in the experiment is 3 Amperes (cut-off value) at which 570 W/cm3 power absorption was observed under an applied electric field strength of (dc) 215 V/cm.
High resolution field emission scanning electron (as is) fracture surface micrograph of 8% Y2O3-ZrO2. No liquid phase formation observed as not deformation of grains is discernible. The grains are equiaxial and of ∼250 nm median grain size, which is indicative of no grain growth.
Variation of tetragonal lattice parameters with time for 8% Y2O3-ZrO2 under (dc) 215 V/cm over the temperature range 600–930 °C. The positive monotonous increase in lattice parameters is due to thermal expansion. The singularities at 847 and 905 °C are due to densification under the action of the imposed thermal and electric fields.
(a) Variation of the tetragonal unit cell volume with time for 8% Y2O3-ZrO2 under (dc) 215 V/cm with time over the temperature range 600–930 °C. At 600 °C, the density of the specimen was 55% which rose to 97% density upon densification under the action of the imposed thermal and electric fields at 905 °C, (b) Close up of the anomalous expansion range from 876–923 °C enabling one to discern 3 distinct stages associated with densification in the vicinity of 905 °C. The range 876–905 °C is the densification range while the 905–923 °C range corresponds to the nonisothermal inelastic relaxation of the anomalous expansion upon the removal of the applied field, (c) comparison of the (103)-(211) peak doublet of the tetragonal phase in the immediate vicinity of 905 °C indicating that no phase transformation is responsible for the observed anomalous lattice expansion.
Variation of the full width at half maximum (FWHM) of tetragonal phase reflections of 8% Y2O3-ZrO2 under (dc) 215 V/cm with time over the temperature range 600–930 °C: (a) (112) and (b) (211). The FWHM data for both reflections exhibit a singularity at 905 °C while the 847 °C singularity is only seen in the FWHM variation of the (112) reflection. An anisotropy in (112) and (211) peak widths of 3:1 magnitude was observed.
Comparison of peak positions of (112)/(200) and (211)/(103) peak clusters under three different circumstances: (i) at RT (25 °C) before densification, (ii) at 923 °C immediately after densification, and (iii) at RT (25 °C) after densification. The residual strains (ε) at room temperature, as computed from tetragonal (112) and (211) reflections, are ε(112) = 0.05% and ε(211) = 0.13%, respectively.
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