Dopant Distributions in Rare‐Earth‐Doped Alumina

Abstract

The distribution of yttrium and lanthanum dopants hason the dopant level, Al 2 O 3 grain size, and impurity content of Al 2 O 3 . been mapped in yttrium-and lanthanum-doped polycrystalline aluminas using imaging secondary-ion mass spec-The objective of this work was to map the yttrium distribution in a 1000-ppm-yttrium-doped polycrystalline Al 2 O 3 samtrometry (imaging-SIMS). Both dopants segregate to grain boundaries and pore surfaces. On average, yttrium occupies ple that has exhibited favorable creep properties. 1 In addition, a 500-ppm-lanthanum-doped sample was examined, primarily to 7.1%-9.0% of the available grain-boundary cation sites, whereas lanthanum occupies only 2.0%-5.2%. In 1000-compare the segregation behavior of the two isovalent rareearth elements and partly to assess the potential of lanthanumppm-yttrium-doped alumina, an abundance of yttrium aluminum garnet precipitates also is observed. Implications of doped Al 2 O 3 for improved creep properties. Mapping of the dopant distributions was performed using these observations to the creep behavior of alumina are discussed. The similarity in the segregation behavior of yttrium a high-resolution scanning-ion microprobe developed at the University of Chicago. 17 This unique instrument uses a finely and lanthanum highlights the potential of lanthanum-doped alumina for improved creep properties.focused gallium beam to sputter secondary ions from the uppermost layers of the sample surface. For many elements, this imaging-SIMS system offers excellent analytical sensitivity,

Atomistic modeling of dopant segregation in α-alumina ceramics: Coverage dependent energy of segregation and nominal dopant solubility

“…Indeed the bulk solubility is below the resolution limit of most experimental methods, the exact value being unknown although it has been reported to be lower than 80 ppm. 1 The results also qualitatively agree with DFT calculations, where H seg of −1.56 eV for 3.3 La/nm 2 were reported for the Σ3 (1 0 · 0) GB, 35 which compares well with −1.89 eV for 3.4 La/nm 2 calculated here. Another study reported H seg of −2.63 eV for 4.2 La/nm 2 at the Σ7 (−1 0 · 2) GB, 36 which again compares reasonably well with −2.34 eV for 4.3 La/nm 2 found in the present study.…”

“…Control over these microstructural parameters in ceramics is typically achieved by a precise control over processing conditions and the use of dopant elements. It is well established that many dopant elements routinely added to ceramics (for example Y, La and Mg in alumina) have, due to their larger ionic size, a low bulk solubility 1 and a marked tendency to segregate to grain boundaries. 2 Once present at interfaces they can affect properties such as interface mobility and transport in the grain boundary plane.…”

Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on Spark Plasma Sintering of transparent alumina

“…The later of densification of ZrO 2 and La 2 O 3 -containing samples is explained by the segregation of the doping agents at grain boundaries (in solid solution and/or as precipitates). Indeed some works have already reported this segregation for all the doping agents considered [10,12,[27][28][29][30][31] during conventional sintering. Thus, the diffusion of the Al ions is reduced and grain boundary sliding is limited.…”

“…Most of these doping agents, due to their very low solubility in alumina, segregate at grain boundaries during the sintering. Some Secondary-Ion Mass Spectrometry (SIMS) images illustrate this phenomenon very clearly; after densification, the doping agent (MgO, La 2 O 3 and Y 2 O 3 ) is located at grain boundaries and pore surfaces [10,11]. For La 2 O 3 and Y 2 O 3 doping, the segregation leads to an inhibition of grain growth and decreases the densification rate [11].…”

Effect of amount of doping agent on sintering, microstructure and optical properties of Zr- and La-doped alumina sintered by SPS

“…Both Zr 4+ and La 3+ cations are larger than Al 3+ cations: their ionic radii are 0.72Å and 1.03Å, respectively for 6-fold coordination compared to 0.53Å for Al 3+ for the same coordination number. 20 Zr 4+ was found to be insoluble in an ␣-alumina lattice 21 and the bulk solubility of La 3+ is really low (∼80 cat ppm 22 ) or even lower. 4 Those doping agents therefore have a strong tendency to segregate at grain boundaries.…”