Near‐Intrinsic Grain‐Boundary Mobility in Dense Yttria

Abstract

Grain-boundary mobilities and grain growth activation energies were measured on high-purity and dense yttria samples annealed in both air and 5%H 2 -N 2 at temperatures ranging from 12001 to 19001C. The grain-boundary mobility for samples annealed in 5%H 2 -N 2 was higher in comparison with air-annealed materials. The measured grain growth activation energy for samples annealed in air was 356735 kJ/mol. For samples annealed in 5%H 2 -N 2 , a transition temperature of 15791C was identified where the grain growth activation energy changed dramatically. The measured activation energies were 373760 and 77072 kJ/ mol for samples annealed at temperatures below and above 15791C, respectively. The increase in activation energy was tentatively attributed to a reduction-induced disordering of the grain boundary corresponding to the temperature at which yttrium metal liquid forms at low oxygen pressures. The data represent the best attempt to measure the near-intrinsic grainboundary mobility for high-purity highly dense yttria. High-resolution transmission electron microscopyand high-angle annular dark field-scanning transmission electron microscopy confirmed that the grain boundaries were clean and free of any observable second phases.

Segregation‐controlled densification and grain growth in rare earth‐doped Y2O3

“…The focus was on segregation driven F I G U R E 1 0 Grain boundary mobility dependent on the inverse annealing temperature determined in this work in comparison to literature data. 29,31,35,43,75,76 All samples were fully densified by FAST/SPS before conducting the thermal treatment in air. The grain boundary mobility was calculated using Equation (2) [Color figure can be viewed at wileyonlinelibrary.com] by elastic effects, that is the size mismatch of dopants.…”

“…42 with where G and G 0 are the average grain size at the time t and t 0 , respectively, n is the grain growth exponent, and K is a temperature-dependent growth factor including a geometrical factor α, the grain boundary energy γ gb , and the grain boundary mobility M gb . As in the literature, 43 the growth coefficient was assumed to be n = 2 as expected for grain boundary migration controlled by the interface reaction. 42,44 High-angle annular dark-field (STEM-HAADF) imaging and STEM-EDX were performed on TEM lamellas which were prepared and thinned by focused ion beam (FIB, FEI STRATA FIB 205).…”

“…withwhere G and G 0 are the average grain size at the time t and t 0 , respectively, n is the grain growth exponent, and K is a temperature‐dependent growth factor including a geometrical factor α , the grain boundary energy γ gb , and the grain boundary mobility M gb . As in the literature, 43 the growth coefficient was assumed to be n = 2 as expected for grain boundary migration controlled by the interface reaction 42,44 …”

A Sucrose‐Mediated Sol–Gel Technique for the Synthesis of MgO–Y2O3 Nanocomposites

“…Ceramics intended for use in infrared (IR) transparent windows need to meet certain criteria that include optical transparency, high mechanical strength, high thermal conductivity, and resistance to thermal shock and erosion . Yttria (Y 2 O 3 ) is an attractive ceramic for optical purposes due to its cubic structure yielding isotropic properties, longer cut‐off wavelength (up to 5 μm) than other optical materials (sapphire, ALON, and spinel), low emissivity, and low scatter . In ceramics like Y 2 O 3 , grain growth can be inhibited by the incorporation of other oxide phases, to give an oxide/oxide composite wherein each phase pins the grain boundaries of the other .…”

“…1 Yttria (Y 2 O 3 ) is an attractive ceramic for optical purposes due to its cubic structure yielding isotropic properties, longer cut-off wavelength (up to 5 lm) than other optical materials (sapphire, ALON, and spinel), low emissivity, and low scatter. [2][3][4][5][6] In ceramics like Y 2 O 3 , grain growth can be inhibited by the incorporation of other oxide phases, to give an oxide/ oxide composite wherein each phase pins the grain boundaries of the other. 7 Consequently, such composite ceramics exhibit improved mechanical characteristics upon consolidation while retaining their optical properties.…”