Phase Stability and Mechanisms of Transformation of La-Doped γ-Alumina

Abstract

We report the phase stability of cubic γ-AlO with respect to lanthanum dopant amount and describe a complete phase transition sequence up to a temperature of 1800 °C, which proceeds from La-doped γ-AlO to LaAlO/γ-AlO to LaAlO. For this purpose, lanthanum contents from 0.81 to 10.0 atom % were incorporated into AlO powders. X-ray diffraction analyses show that only γ-AlO phase was present after heat treatment at 1000 °C for 2 h with 0.81, 1.68, 2.24, and 2.62 atom % lanthanum concentrations. The phase stabilization can be mainly attributed to the combined effects of small crystallite size of the AlO powders and the presence of the lanthanum dopant, which occupies the AlO octahedral sites. At compositions of 3.63, 5.00, 7.49, and 10.0 atom %, the amount of LaAlO phase formed by the solid phase reaction between AlO and La ions becomes detectable under X-ray diffraction.

Increased Hydrogenation Rates in Pd/La-Al2O3 Catalysts by Hydrogen Transfer O(-La) Sites Adjacent to Pd Nanoparticles

“…In general, when elements with larger radii are incorporated, the diffraction peaks shift to a lower angle. However, the diffraction peak may shift to a high angle due to lattice distortion and stress, which is also found in other oxides doped with rare-earth elements. , In the XRD pattern of La-Al 2 O 3 , some weak peaks (23.4, 33.4, 41.2, 47.9, 59.7, and 70.1°) belonging to LaAlO 3 (JCPDS 31-0022) emerge in addition to the dominant peak of alumina, deriving from the solid-phase reaction between alumina and La 3+ . , The weak single peak at 2θ = 29.1° could be due to the trace formation of La 2 O 3 (JCPDS 83-1345). The appearance of LaAlO 3 and La 2 O 3 may relate to the aggregation of random dispersed La atoms as seen in the STEM image.…”

Foreign element doping and thermal stability of alumina aerogels

“…For the SA, since the mullitization totally changed the phase transforming route, the mullite and θ-Al 2 O 3 instead of α-Al 2 O 3 were observed at 1300 • C. The LA remained metastable alumina at 1200 • C and evolved to α-Al 2 O 3 and LaAl 11 O 18 at 1300 • C, which is typical in a La 2 O 3 -Al 2 O 3 system with small amount of lanthanum. 24 It suggested that there was a chemical reaction between the alumina and lanthanum oxide. Both the SA and LA generated new substances after calcination at 1300 • C; however, the lanthanum addition is not able to effectively restrain the formation of α-Al 2 O 3 at this temperature.…”

“…Unlike Si 4+ with a smaller ionic radius of 0.04 nm, 35 since the radius of La 3+ (0.103 nm) is nearly twice that of Al 3+ (0.054 nm), it has poor solubility in the alumina. 24 Therefore, too much La 3+ in the LA would lead to unexpected precipitation and sintering. That is to say, too much of La in alumina would conversely harm its thermal stability.…”

Alumina applied in bone regeneration: Porous α-alumina and transition alumina

“…Alumina, also known as corundum [28], is a ceramic material widely used in various applications due to its excellent mechanical and physicochemical properties, such as high hardness, high wear resistance, low thermal conductivity, high corrosion resistance, high chemical and electrical resistance [24,28,29]. In most published papers, authors refer to the α-alumina (α-Al 2 O 3 ) phase simply as alumina (Al 2 O 3 ) or corundum.…”

“…Despite several efforts involving the use of alumina-based materials in bone repair devices, there are still debates about the effect of alumina on bioactivity and osseointegration. Alumina varies from the amorphous phase to α-alumina (the most thermodynamically stable crystalline phase), where other metastable crystalline forms are also possible (χ, η, δ, κ, θ, γ, ρ), which are commonly called transition aluminas [24]. They differ in surface features, notably topography, surface area, and reactivity.…”