Chemistry

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Oxazolium Salts as Organocatalysts for the Umpolung of Aldehydes
(ACS Publications, 10/1/2018) Garapati, Venkata Krishna Rao; Gravel, Michel
Oxazolium salts were successfully employed for the first time as organocatalysts for benzoin, Stetter, and redox esterification reactions. An N-mesityl oxazolium salt catalyzed homobenzoin reaction of aromatic, heteroaromatic, and aliphatic aldehydes delivered α-hydroxy ketones in high yields. This new type of catalyst proved remarkably effective for the Stetter reaction of challenging substrates such as β-alkyl-α,β-unsaturated ketones and electron-rich aromatic aldehydes in comparison to common thiazolium and triazolium salts.
Connecting Molecular Conformation to Aggregation in P3HT Using Near Edge X-ray Absorption Fine Structure Spectroscopy
(American Chemical Society, 10/11/2017) Martinson, Mercedes; Urquhart, Stephen; Eger, Shaylin; Murcia, Victor; Ade, Harald; Collins, Brian
Carbon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) and UV-vis spectroscopy are used to examine differences between highly aggregated and poorly aggregated forms of the polymer poly(3-hexylthiophene) (P3HT), based on as-cast and annealed regio-random and regio-regular P3HT samples. UV-vis spectra show characteristic signatures of unaggregated P3HT in regio-random P3HT, and of H-aggregation in regio-regular P3HT samples. Distinct spectroscopic differences, including energy shifts, are observed in the NEXAFS spectra of aggregated P3HT relative to the unaggregated forms. These differences are reproduced with Transition – Potential Density Functional Theory (TP-DFT) calculations which explore aggregation and molecular confirmation. Differences in the NEXAFS spectra of P3HT are assigned to thiophene backbone twisting in the unaggregated forms of P3HT, and to various degrees of chain planarization in aggregated forms of P3HT that also correlate to the exciton bandwidth. These results open up the prospect of charactering conformation and related difficult to assess structural details through NEXAFS spectroscopy and correlative theory and electronic structure analysis.
Temperature Dependence in the NEXAFS Spectra of n-Alkane
(American Chemical Society, 11/16/2018) Urquhart, Stephen; Perera, Sahan; Sadegh, Shokatian; Wang, Jian
The near edge X-ray absorption fine structure (NEXAFS) spectra of orthorhombic single crystals of n-octacosane (n-C28H58), recorded at room temperature (298 K) and at cryogenic temperatures (93 K), show distinct differences. The characteristic carbon 1s → σ*C–H band in the NEXAFS spectrum of n-C28H58 is broader and has a lower-energy onset in its room temperature spectrum than in its NEXAFS spectrum recorded at cryogenic temperatures. Density functional theory simulations show that nuclear motion and molecular disorder contribute to the observed spectral broadness and are the origin of the low-energy onset of the C–H band in the room temperature spectrum
Enantioselective Stetter Reactions Catalyzed by Bis(amino)cyclopropenylidenes: Important Role for Water as an Additive
(ACS Publications, 12/15/2020) Rezazadeh Khalkhali, Mehran; Wilde, Myron M. D.; Gravel, Michel
The first highly enantioselective intermolecular Stetter reaction using simple enones is reported. A series of novel chiral BAC structures were designed and prepared. They were tested in the Stetter reaction with simple aldehydes and enones. The products were generated in excellent yields and enantioselectivities (up to 92% ee). Surprisingly, a substoichiometric amount of water was crucial to obtain high enantioselectivities. Chiral BACs were also shown to catalyze 1,6-conjugate addition reactions with paraquinone methides enantioselectively.
in situ X-ray Absorption Spectroscopic Analysis of Gold-Palladium Bimetallic Nanoparticle Catalysts
(American Chemical Society, 2013) MacLennan, Aimee; Banerjee, Abhinandan; Hu, Yongfeng; Miller, Jeffrey T; Scott, Robert WJ
Gold–palladium core–shell nanoparticles have been previously shown to be extremely effective catalysts for a number of oxidation reactions including the aerobic oxidation of alcohols. However, the novel activity and durability of such catalysts are still poorly understood, and there are several putative mechanisms by which oxidation reactions can proceed. Previously we showed that Pd(II) salts in the presence of Au nanoparticles were also effective catalysts for the room temperature oxidation of crotyl alcohol. Herein we show an in situ X-ray absorption spectroscopy (XAS) study at both the Pd–K and Pd-LIII edges of Au nanoparticle/Pd(II) salt solutions in the presence of crotyl alcohol. Liquid cells with X-ray permeable windows were used to obtain quick-scan XAS data during the oxidation of crotyl alcohol, allowing for time-resolved Pd speciation information and information about the reaction mechanism and kinetics. XAS measurements definitively show that the first step of this reaction involves Pd reduction onto the Au nanoparticles; in addition, further studies of the stability of the resulting Au–Pd core–shell nanoparticles toward oxygen gas suggests that the role of Au in such catalysts is to prevent the reoxidation of the catalytically active surface Pd atoms. Catalytic crotyl alcohol oxidation measurements were done which validated that the in situ reduction of Pd(II) in the presence of Au nanoparticles did indeed result in catalytically active AuPd bimetallic catalysts.
Following the Thermal Activation of Au25(SR)18 Clusters for Catalysis by X-Ray Absorption Spectroscopy
(American Chemical Society, 2013) Shivhare, Atal; Chevrier, Daniel; Purves, Randy W; Scott, Robert WJ
We show the thermal activation of phenylethanethiolate (L = SC8H9) and hexanethiolate (L = SC6H13) Au25L18 monolayer protected clusters (MPCs) on carbon black supports, followed by characterization with extended X-ray absorption fine structure (EXAFS) spectroscopy and transmission electron microscopy (TEM). EXAFS analysis shows that the thiolate stabilizers can be partially removed from the surface under mild heating conditions without significant changes in the cluster size. The resulting clusters are shown to be catalytically active for the reduction catalysis of 4-nitrophenol. EXAFS and TEM data show that thermal treatment under air at 200 °C leads to nearly complete removal of all of the thiolate stabilizers with little to no growth in cluster size, while cluster sintering was seen at higher calcination temperatures. The maximum catalytic activity for Au25(SC8H9)18 MPCs was seen at 250 °C activation conditions. These results are consistent with results reported earlier for Au25(SR)18 clusters on ceria by Jin et al., who suggested that cluster integrity was maintained during mild activation conditions. Here, EXAFS data unambiguously show that while the cluster size does not grow significantly, such mild heating conditions do lead to nearly complete removal of the thiolate stabilizers.
Watching Iron Nanoparticles Rust: An In Situ X-ray Absorption Spectroscopic Study
(American Chemical Society, 2014) Yao, Yali; Hu, Yongfeng; Scott, Robert WJ
Iron nanoparticles and iron oxide nanoparticles are among the most commonly studied nanomaterials because of their applications in fields ranging from catalysis to ferrofluids. However, many synthetic methods give iron nanoparticles with large size distributions, and it is difficult to follow the kinetics of iron nanoparticle oxidation reactions and the relative speciation of iron oxidation states in real time. Herein, we introduce a simple approach of controlling the sizes of Fe@FexOy nanoparticles and a novel method for following Fe@FexOy nanoparticle oxidation in situ in liquid solutions by Fe K- and L-edge X-ray absorption near-edge structure (XANES) spectroscopy. XANES results show that these Fe@FexOy nanoparticles have similar XANES spectra before exposure to air. In situ XANES measurements allow for quantitative oxidation kinetics of different nanoparticle sizes to be followed; results show that the rate of Fe(0) oxidation increases with a decrease in average nanoparticle size. However, the rate of Fe core size depletion was found to be ca. 0.02 nm/min for all the nanoparticle systems studied. This suggests similar oxidation mechanisms are at work for all the particle sizes studied. This work shows that in situ liquid cell XANES can be used to follow oxidation state and coordination environment changes in Fe NP dispersions.
Design, synthesis, catalytic application, and strategic redispersion of plasmonic silver nanoparticles in ionic liquid media
(Elsevier, 2014) Banerjee, Abhinandan; Theron, Robin; Scott, Robert WJ
Silver nanoparticles synthesized in tetraalkylphosphonium ionic liquids are found to be excellent catalysts for borohydride-induced reductive degeneration of Eosin-Y, a dye that has been classified as a Class 3 carcinogen by the International Agency for Research on Cancer. TEM images indicated that the size of the Ag nanoparticles was significantly influenced by heat-induced sintering. A strategy was devised to redisperse smaller Ag nanoparticles from their aggregated/sintered counterparts via a two-step protocol that involved oxidative etching of Ag nanoparticles, followed by a re-reduction step. This protocol led to a reduction in the sintered Ag nanoparticle size from 15.7 ± 6.1 nm to 3.7 ± 0.8 nm, which was consistent with the size of the as-synthesized nanoparticles. The as-synthesized and the redispersed Ag nanoparticles were found to catalyze the bleaching of Eosin-Y with comparable efficiencies; first order rate constants for Eosin Y reduction were ∼8 times higher for smaller Ag nanoparticles compared to their sintered counterparts. An examination of the kinetics of Ag nanoparticle etching was performed via temperature-controlled UV–vis spectroscopy. Changes in the oxidation state of Ag during this sequence of events were also followed by in situ X-ray absorption spectroscopy of Ag nanoparticles in the ionic liquid.
An investigation of the thermal stability of NdxYyZr1 x yO2 d inert matrix fuel materials
(Elsevier, 2015) Hayes, John; Grosvenor, Andrew; Saoudi, Mounda
An important step in achieving a closed uranium fuel cycle is to develop new inert matrix fuel (IMF) materials for use in the burn-up of transuranic species (TRU; i.e., Pu, Np, Am, Cm). Cubic fluorite zirconia (ZrO2) has ideal properties for use in IMF applications, but it is not stable at room temperature and must be stabilized through the addition of small amounts of dopants such as Y. While Y-substituted zirconia (YSZ) has been extensively studied, relatively little work has been done to investigate how the addition of an actinide to the YSZ system affects the properties of these materials. To this end, the long-range and local structures of a series of NdxYyZr1 x yO2 d compounds (Nd was used as a surrogate for Am) were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption spectroscopy (XAS) at the Zr K-, Zr L3-, Y K-, and Nd L3-edges. The thermal stability of Nd–YSZ materials was also investigated by annealing the materials at temperatures ranging between 600 and 1400 °C. These studies showed that the thermal stability of the NdxYyZr1-x-yO2-d system was improved by the addition of small amounts of Y (i.e. 5 at.%) to the system. Additionally, the XAS results showed that the local structure around Zr remained relatively constant; only changes in the second coordination shell were observed when the materials were annealed. These results strongly suggest that the addition of Y can significantly improve the thermal stability of zirconia-based IMFs. This study has also confirmed the importance and value of using advanced characterization techniques that are sensitive to the local struc- tures of a material (i.e., XAS).
Isolation of Carboxylic Acid-Protected Au25 Clusters using a Borohydride Purification Strategy
(American Chemical Society, 2015) Shivhare, Atal; Wang, Lisa; Scott, Robert WJ
We report the synthesis of 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHA) protected Au25 clusters with moderate yields (∼15%) using a NaBH4 purification strategy. UV–vis spectroscopy, transmission electron microscopy (TEM), and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry were employed to study the entire process of the isolation of 11-MUA-protected Au25 clusters from a polydisperse Au cluster solution. UV–vis and TEM data clearly show the formation of a polydisperse mixture, which upon the addition of NaBH4 leads to the growth and precipitation of non-Au25 clusters, leaving the Au25 clusters behind. MALDI MS shows the molecular ion peak for the 11-MUA-protected Au25 cluster. 11-MUA-protected Au25 clusters in THF were purified by slowly increasing the pH of the solution, which leads to the complete deprotonation of carboxyl groups on the surface and eventually precipitation of Au25 clusters. Further protonation of these clusters by acetic acid leads to their solubilization in THF. These results show that, owing to the inherent stability of Au25 clusters, a NaBH4 purification strategy can be used to isolate Au25 clusters with surface carboxylic acid functionalities from a polydisperse Au cluster solution.
Optimization of transition metal nanoparticle- phosphonium IL composite catalytic systems for deep hydrogenation and hydrodeoxygenation reactions
(Royal Society of Chemistry, 2015) Banerjee, Abhinandan; Scott, Robert WJ
A variety of metal nanoparticle (NP)/tetraalkylphosphonium ionic liquid (IL) composite systems were evaluated as potential catalysts for the deep hydrogenation of aromatic molecules. Particles were synthesized by reducing appropriate metal salts by LiBH4 in a variety of ILs. Gold NPs were used as probes to investigate the effect of both chain lengths of the alkyl substituents on the phosphonium cation and the nature of anions, on the stability of NPs dispersed in the ILs. The presence of three medium-to-long alkyl chains (such as hexyl) along with one long alkyl chain (such as tetradecyl) in the IL, coupled with highly coordinating anions (such as halides, or to a smaller extent, bis-triflimides) produced the most stable dispersions. These ILs also showed maximum resistance to heat-induced sintering; for example, TEM studies of Pt NPs heated under hydrogen to 120 °C showed only moderate sintering in trihexyl(tetradecyl)phosphonium chloride and bis(triflimide) ILs. Finally, olefinic hydrogenations, aromatic hydrogenations, and hydrodeoxygenation of phenol were carried out with Ru, Pt, Rh and PtRh NPs using hydrogen at elevated pressures. From preliminary studies, Ru NPs dispersed in trihexyl(tetradecyl)phosphonium chloride emerged as the catalyst system of choice. The presence of borate Lewis-acid by-products in the reaction medium (from the borohydride reduction step) allowed for partial phenol hydrodeoxygenation.
Probing the effect of radiation damage on the structure of rare-earth phosphates
(Elsevier, 2015) Rafiuddin, Mohamed Ruwaid; Grosvenor, Andrew
Synthetic analogues of naturally occurring monazite (REPO4; RE = La to Gd) and xenotime (RE0PO4; RE0 = Tb to Lu and Y) minerals have been identified as potential wasteforms for nuclear waste. High energy ion-implantation of crystalline materials simulates radiation-induced structural damage and allows for the radiation resistance of a crystal structure to be probed. The structural stability of Au ion- implanted La1-xYbxPO4 materials was investigated using micro-X-ray diffraction (m-XRD) and glancing angle X-ray absorption near-edge spectroscopy (GA-XANES) in this study. The long- and short-range order of La1-xYbxPO4 (x = 0, 0.3, 0.7, 1.0) is affected by ion-implantation and, thus, the materials are prone to structural damage. The structures of some members of the La1-xYbxPO4 series (x = 0.7 and 1.0) were observed to partially recover after being implanted with Au ions to a high dose. The structures of all members of the La1-xYbxPO4 series were observed to recover from damage resulting from ion- implantation after annealing the materials at temperatures >300 C.
Investigating the Geochemical Model for Molybdenum Mineralization in the JEB Tailings Management Facility at McClean Lake, Saskatchewan: An X‐ray Absorption Spectroscopy Study
(American Chemical Society, 2015) Blanchard, Peter; Hayes, John; Grosvenor, Andrew; Rowson, John; Hughes, Kebbi; Brown, Caitlin
The geochemical model for Mo mineralization in the JEB Tailings Management Facility (JEB TMF), operated by AREVA Resources Canada at McClean Lake, Saskatchewan, was investigated using X-ray Absorption Near-Edge Spectroscopy (XANES), an elemental-specific technique that is sensitive to low elemental concentrations. Twenty five samples collected during the 2013 sampling campaign from various locations and depths in the TMF were analyzed by XANES. Mo K-edge XANES analysis indicated that the tailings consisted primarily of Mo6+ species: powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3·8H2O), and molybdate adsorbed on ferrihydrite (Fe(OH)3 − MoO4). A minor concentration of a Mo4+ species in the form of molybdenite (MoS2) was also present. Changes in the Mo mineralization over time were inferred by comparing the relative amounts of the Mo species in the tailings to the independently measured aqueous Mo pore water concentration. It was found that ferrimolybdite and molybdate adsorbed on ferrihydrite initially dissolves in the TMF and precipitates as powellite.
Rational Design and Characterization of Bimetallic Gold-Palladium Nanoparticle Catalysts
(Wiley, 2015) Scott, Robert WJ
This feature article covers a long‐term project in our laboratory at the University of Saskatchewan towards the rational synthesis of controlled‐architectures of gold‐palladium bimetallic nanoparticle catalysts for use as low‐temperature alcohol oxidation catalysts. Syntheses involve controlled growth of nanoparticle architectures via solution‐based nanoparticle synthetic strategies, followed by deposition of the designed particles onto solid supports. In addition, characterization methods used to elucidate structures of the synthesized particles before and after activation for catalysis will be discussed. This includes traditional characterization methods such as transmission electron microscopy and X‐ray absorption fine structure spectroscopy (EXAFS), but also includes, more recently, the use of in situ X‐ray absorption spectroscopy studies of gold‐palladium nanoparticle catalysts. Strategies and challenges towards the rational synthesis of heterogeneous supported‐nanoparticle catalysts based on bimetallic nanoparticle precursors will be detailed and contrasted with more traditional routes to synthesize such catalytic materials.
Following the Reactivity of Au25(SC8H9)18 - Clusters With Pd2+ and Ag+ Ions Using in Situ X-ray Absorption Spectroscopy: A Tale of Two Metals
(American Chemical Society, 2015) Shivhare, Atal; Lee, Kee Eun; Hu, Yongfeng; Scott, Robert WJ
This work examines the reaction between Au25(SC8H9)18– clusters with palladium acetate (Pd2+) and silver nitrate (Ag+) using UV–vis, transmission electron microscopy (TEM), extended X-ray absorption spectroscopy (EXAFS), and in situ liquid cell X-ray absorption spectroscopy (XAS). UV–vis results show that upon the addition of Pd2+ and Ag+ salts to Au25(SC8H9)18– clusters significant changes are seen in the optical properties of the clusters. In the case of Pd, there is little to no change in the size of the clusters evidenced by TEM, while for Ag systems, significant particle growth is seen. In situ XAS results show that Pd2+ reacts with the staple motifs of Au25(SC8H9)18– clusters and forms Pd(II) thiolate species, as shown by the Pd L3- and Au L3-edge data as well as Pd K-edge EXAFS results. However, Ag L3-edge data suggest that Ag+ reduces to Ag on the cluster core and does not form Ag(I) thiolate species. This work highlights the power of using in situ XANES to follow Au cluster transformations in liquid environments.
In situ X-ray Absorption Spectroscopic Study of Fe@FexOy/Pd and Fe@FexOy/Cu Nanoparticle Catalysts Prepared by Galvanic Exchange Reactions
(American Chemical Society, 2015) Yao, Yali; Patzig, Christian; Hu, Yongfeng; Scott, Robert WJ
Fe@FexOy core–shell nanoparticles have been previously shown to be a versatile support for catalytic metals such as Pd and Cu. However, the resulting structure, metal speciation, and performance of such catalysts in catalytic reactions are still poorly understood. Herein, we synthesize Fe@FexOy-supported Pd and Cu nanoparticles by controlling the molar ratios of Fe@FexOy nanoparticles to Pd2+ or Cu2+ species. Scanning transmission electron microscopy analyses show that Pd or Cu NPs are deposited on the exterior shell of the Fe@FexOy nanoparticles. In situ X-ray absorption near-edge structure (XANES) spectra were used to follow the formation processes of Fe@FexOy/Pd and Fe@FexOy/Cu nanoparticles and the performance of Fe@FexOy/Pd nanoparticles for Suzuki–Miyaura cross-coupling reactions. The results show that different molar ratios of Fe@FexOy nanoparticles to Pd2+ or Cu2+ lead to different morphologies of the resulting supported-NP structures. In situ XANES results show that Fe@FexOy nanoparticles can effectively fully reduce Pd or Cu salts over the course of ∼20 min to give small Pd or larger Cu nanoparticles on the surface and can also rereduce oxidized Pd in Suzuki–Miyaura cross-coupling reactions.
A study of the electronic structure and structural stability of Gd2Ti2O7 based glass-ceramic composites
(the Royal Society of Chemistry, 2015) Aluri, Esther Rani; Grosvenor, Andrew
Glass-ceramic composite materials have been investigated for nuclear waste sequestration applications due to their ability to incorporate large amounts of radioactive waste elements. Borosilicate- and Fe–Al–borosilicate glass-ceramic composites containing pyrochlore-type Gd2Ti2O7 crystallites were synthesized at different annealing temperatures and investigated by multiple techniques. Backscattered electron (BSE) images were collected to investigate the interaction of the pyrochlore crystallites with the glass matrix. Examination of the X-ray absorption near edge spectroscopy (XANES) spectra from the composite materials has shown how the glass composition, pyrochlore loading, and annealing temperature affects the chemical environment around the metal centers. These investigations have shown that the Gd2Ti2O7 crystallites can dissolve in the glass matrix depending on the glass composition and annealing temperature. The borosilicate glass composite materials were implanted with high-energy Au ions to mimic radiation induced structural damage. Surface sensitive glancing angle XANES spectra collected from the implanted composite materials have shown that structural damage of Gd2Ti2O7 occurs as a result of implantation, and that these materials show a similar response to ion implantation as Gd2Ti2O7 alone.
Investigation of NdxY0.25–xZr0.75O1.88 inert matrix fuel materials made by a co-precipitation synthetic route
(NRC Research Press, 2016) Hayes, John; Grosvenor, Andrew
Yttria-stabilized zirconia (YSZ) is a material that is being considered for use as an inert matrix fuel in nuclear reactors, but a complete characterization of these materials is required for them to be licensed for use. A series of NdxY0.25–xZr0.75O1.88 materials have been synthesized using a co-precipitation method, and the thermal stability of these materials has been studied by annealing them at 1400 and 1500 °C. (Nd was used as surrogate for Am.) The long-range and local structures of the materials were characterized via powder X-ray diffraction, scanning electron microscopy, wavelength dispersive spectroscopy, and X-ray absorption spectroscopy at the Zr K- and Y K-edges. These results were compared with the previous characterization of Nd-YSZ materials synthesized using a ceramic method. The results indicated that the ordering in the local metal–oxygen polyhedral remains relatively unaffected by the synthetic method, but there was increased long-range disorder in the materials prepared by the co-precipitation method. Further, it was found that the materials produced by the co-precipitation method were unexpect- edly unstable when annealed at high temperature. This study highlights the importance of determining the effect of synthetic method on material properties and demonstrates how the co-precipitation route could be used to produce inert matrix fuels.
Silicon 1s Near Edge X-ray Absorption Fine Structure Spectroscopy of Functionalized Silicon Nanocrystals
(American Chemical Society, 2016) Ritchie, Andrew; Cao, Wei; Dasog, Mita; Purkait, T.K.; Senger, Curtis; HU, Yongfeng; Xiao, Q.F.; Veinot, Jon; Urquhart, Stephen; Urquhart, Stephen
Silicon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of silicon nanocrystals have been examined as a function of nanocrystal size (3 – 100 nm), varying surface functionalization (hydrogen or 1-pentyl termination), or embedded in oxide. The NEXAFS spectra are characterized as a function of nanocrystal size and surface functionalization. Clear spectroscopic evidence for long range order is observed Si-NCs that are 5-8 nm in diameter or larger. Energy shifts in the silicon 1s NEXAFS spectra of covalently functionalized silicon nanocrystals with changing size are attributed to surface chemical shifts and not to quantum confinement effects.
Investigation of the Thermal Stability of NdxScyZr1−x−yO2−δ Materials Proposed for Inert Matrix Fuel Applications
(American Chemical Society, 2016) Hayes, John; Grosvenor, Andrew; Saoudi, Mouna
Inert matrix fuels (IMF) consist of transuranic elements (i.e., Pu, Am, Np, Cm) embedded in a neutron transparent (inert) matrix and can be used to “burn up” (transmute) these elements in current or Generation IV nuclear reactors. Yttria-stabilized zirconia has been extensively studied for IMF applications, but the low thermal conductivity of this material limits its usefulness. Other elements can be used to stabilize the cubic zirconia structure, and the thermal conductivity of the fuel can be increased through the use of a lighter stabilizing element. To this end, a series of NdxScyZr1−x−yO2−δ materials has been synthesized via a co-precipitation reaction and characterized by multiple techniques (Nd was used as a surrogate for Am). The long-range and local structures of these materials were studied using powder X-ray diffraction, scanning electron microscopy, and X-ray absorption spectroscopy. Additionally, the stability of these materials over a range of temperatures has been studied by annealing the materials at 1100 and 1400 °C. It was shown that the NdxScyZr1−x−yO2−δ materials maintained a single cubic phase upon annealing at high temperatures only when both Nd and Sc were present with y ≥ 0.10 and x + y > 0.15.

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