Typical Sintering Temperatures Research Articles

Atomistic structures and stabilities of MgAl2O4 surfaces under processing conditions: A first-principles thermodynamics study

Surfaces, in contacting ambient environments, are of particular importance for controlling sintering, thin-film growth, and catalytic activity of oxides. Magnesium aluminate spinel (MgAl2O4), an essential oxide for both functional and structural ceramics, has attracted considerable attentions across diverse scientific fields. Nonetheless, a central challenge in rationally manipulating the properties of MgAl2O4 lies in the atomistic understanding of its surface structures under processing conditions. This study presents comprehensive first-principles calculations of MgAl2O4 (110) and (111) polar surfaces with/without off-stoichiometries. We predict from a thermodynamic model the dependence of surface stabilities on critical processing parameters, namely the oxygen partial pressure (PO2) and temperature (T). The findings indicate that at typical sintering temperatures, the non-stoichiometric (110) surface transits from Al/Mg-rich to O-rich with increasing PO2. In contrast, the non-stoichiometric (111) surface stably terminates in a Mg-rich configuration at low PO2, gradually shifting to Al-rich and then to Mg/O-rich as PO2 increases. The correlation between surface off-stoichiometry and stability is elucidated through electronic structure analysis. The investigation offers fundamental insights into surface structures and physicochemical behavior of MgAl2O4, thereby facilitating the rational processing control of complex oxides for applications in catalysis and electronics.

Thermodynamics for the non-conventional synthesizing of out-of-plane ordered double-transition metal “312” and “413” MAX phases (o-MAX): A high throughput linear programing first-principles calculation

• Temperature corrections at the typical sintering temperature were addressed properly. • A strong correlation between actual formability of o-MAX phases and the DOS at the Fermi level were found. • Using an updated linear programing optimization algorithm, results of the preparation of o-MAX phase in the existing experiments can be predicted well. • New non-conventional synthetic routes were suggested, expected to improve purity and yield. The reaction thermodynamics for synthesizing the “312” and “413” o-MAX phases using the powder metallurgy are investigated using a linear programing optimization algorithm based on the high-throughput first principles phonon calculations. The validity and reliability of the current methodology are verified by correctly predicting the impurities in four experimentally known o-MAX systems including Cr-Ti-Al-C, Cr-V-Al-C, Mo-Sc-Al-C and Mo-Ti-Al-C. The formability of each investigated o-MAX phase is evaluated by means of formation enthalpy and formation Gibbs free energy in a temperature range from 0 K to 1700 K. It is revealed that the thermodynamic stability of the “413” o-MAX structure is no better than that of the “312” phase. The formability of “413” o-MAX is also reduced at high sintering temperature, compared to that of “312” phase. The optimal synthetic routes are predicted for all thermodynamically stable “312” and “413” o-MAX phases. It is found that most o-MAX phases considered could be prepared as the single phase using the non-conventional synthetic routes from the aspect of reaction thermodynamics. Few of them including Cr 2 TaAlC 2 , Nb 2 HfAlC 2 , Nb 2 TaAlC 2 , Nb 2 Hf 2 AlC 3 , Nb 2 Ta 2 AlC 3 , Mo 2 V 2 AlC 3 and Mo 2 Ta 2 AlC 3 are predicted to be either destabilized at high temperature or overwhelmed by the most competing side reaction.

Mass transport in binary TiO2:SiO2 and GeO2:SiO2 direct ink write glasses

AbstractThe mass transport mechanisms of Ti in TiO2:SiO2 and Ge in GeO2:SiO2 direct ink write, additively manufactured glasses were studied. Due to the low solubility of Ti in SiO2 and high melting point of TiO2 relative to SiO2, Ti transport was found to occur via solid state interdiffusion between adjoining SiO2 and TiO2 precursor particles. The diffusivity of titanium in SiO2 measured over typical sintering temperatures (1000–1300°C) using Rutherford backscattering spectrometry was . This provides an estimate of ∼30 nm for the diffusion length under typical sintering conditions (2 h at 1200°C). Although Ti and Ge have similar diffusivities in SiO2 glass at low concentrations, GeO2 was found to be much more mobile during the sintering of printed GeO2:SiO2 green bodies. This was evident in glasses with phase separated GeO2 regions over length scales of ∼10 µm and in experiments involving binary xerogel films in which GeO2 migrated over ∼10 µm through cracked, porous SiO2 layers. Large phase separated regions and long transport lengths in GeO2:SiO2 suggest that the transport of GeO2 occurs prior to the densification of the SiO2 matrix via an alternative mechanism such as capillary flow. These results inform important considerations in the design of index modifying inks for the direct ink write process, namely initial precursor phase, mutual solubility with the base SiO2 glass, and mass transport throughout the sintering process.

Sr and Co Vapor-Phase Transport from LSCF Cathodes

Strontium transport contributes to degradation mechanisms in SOFCs, especially strontium zirconate formation at the interface of the cathode barrier layer with the YSZ electrolyte. High temperatures required for cathode sintering lead to Sr transport during cell construction. SEM analysis of SOFCs with LSCF cathodes shows Sr at the YSZ/GDC barrier layer interface, but no Sr throughout the GDC barrier layer itself, as would be expected for solid-phase transport. Vapor-phase transport was identified as a possible mechanism that would lead to these observations. A series of tests were performed to differentiate between surface diffusion and vapor-phase diffusion of species from LSCF cathode material at typical sintering temperatures (up to 1100°C). A GDC substrate was printed with LSCF and separated by an air gap from a YSZ target substrate. First a simple spacer ring was used to create the air gap, and strontium transport was observed via SEM-EDS (energy dispersive spectroscopy). Then, various geometries with long surface paths were employed to reduce the possibility of surface transport. The target substrates were analyzed via x-ray photoelectron spectroscopy (XPS) with high sensitivity for surface species. An open air gap did not show evidence of Sr or Co transport. A refined, enclosed air gap with long surface path length did show such evidence for Sr and Co, indicating an enclosed area to maintain significant vapor pressure was necessary for transport. An SOFC with LSCF in direct contact with a barrier layer would also provide such an environment for vapor-phase transport to occur. Furthermore, spatially resolved analysis showed a relatively uniform distribution of Sr and Co across the target substrate. This supports the vapor-phase mechanism as Sr and Co transported via surface diffusion would have been fixed preferentially to the outer edge of the target substrate. These results have implications for adjusting sintering conditions and barrier layer requirements to prevent the formation of undesired strontium zirconate. This work was performed for the US DOE Office of Fossil Energy’s Solid Oxide Fuel Cell program under the Cathode Task.

Optimization of Contact Cathode Composition Based on La0.8Sr0.2MnO3±δ for SOFC Stacks

A stack based on planar solid oxide fuel cells (SOFCs) is an assembly of ceramic plates - membrane-electrode assemblies (MEA) and metal current collectors, which play the role of the distribution of gas mixtures over the electrode area, as well as current collection. In order to organize the high-quality current collection it’s necessary to provide a reliable electrical contact between the MEA’s electrodes and contact surfaces of the current collectors. Electrical contact between MEAs’ anode electrode and the collector is achieved by pressing the contact nickel meshes. Metal-based conductive adhesives are also used to reduce the contact resistance at the anode electrode. Despite this in order to ensure contact between the MEA’s cathode electrode and the collector this approach is not applicable due to the rapid oxidation of contact meshes in air atmosphere at high temperatures. In turn, contact pastes based on conductive ceramics do not have such a drawback and make it possible to ensure reliable contact under the conditions of the SOFC cathode chamber.Materials for the contact adhesive for the SOFC cathode chamber must be chemically and thermomechanically compatible with the materials of the SOFC cathode and bipolar plate along with high electrical conductivity. These requirements are met by materials based on lanthanum strontium manganite oxide (LSM) materials, which are widely used as cathode materials for SOFCs. It should be noted that the contact adhesive must also correspond to the limitations of technological processes of SOFC stack manufacturing. SOFC stacks are sealed with glass in a temperature range of 930-950°C, so it’s necessary to use a material that forms a conductive contact at temperatures not higher than 950°C, which is significantly lower than typical sintering temperatures of LSM-based cathode.The synthesis of single-phase highly dispersed powders with the composition of La0.8Sr0.2MnO3±δ (LSM) and (La0.8Sr0.2)0.97MnO3±δ (LSM-d) was carried out by the glycine-nitrate method. After synthesis some of the obtained materials were ball-milled in ethanol using 5 mm ceramic milling bodies at a speed of 600 rpm for 300 and 600 min. A mixture of polyvinyl butyral, toluene, and butanol was used as the basis for the contact paste.Tests of the electrical conductive properties of contact pastes were carried out in air in temperature range of 600-950°C. Samples were kept for 2 hours before cooling at the maximum temperature. Figure shows the results of resistivity measurements: the dashed lines represent the values obtained when the sample was cooled.The maximum values of the resistivity at a temperature of 850°C were obtained for contact adhesive samples based on non-activated stoichiometric (LSM) and A-deficient (LSM-d) powders. Low electrical conductivity can be associated with weak intergranular contact due to the strong agglomeration of the material after synthesis. Grinding for 300 minutes results in a noticeable reduction in the resistivity of the contact adhesive (LSM-300). Change in resistivity after holding at maximum temperature, as well as the change in the slope of the temperature dependence of the resistivity of the adhesive based on LSM-300 indicates the sintering of the contact adhesive powder into a ceramic compact, which is confirmed by SEM results. In turn, holding at a temperature of 950°C of contact adhesive based on LSM-600 (600 min grinding pre-activated) powder does not lead to its sintering.Grinding of the initially single-phase LSM powder results in the appearance of additional reflections in the XRD-spectrum corresponding to the Sr(OH)2 and MnCO3 phases. An increase in the grinding time leads to an increase in the proportion of impurity phases that prevent the contact adhesive from sintering at temperatures <950°C.Thus, the best results were shown by a contact adhesive based on stoichiometric LSM powder, pre-activated by grinding for 300 minutes. Holding at a temperature of 950°C leads to sintering of LSM-300 powder into ceramics, which makes it possible to form a reliable electrical contact under the conditions of the SOFC cathode chamber.We have proposed a method for the manufacture and deposition of a contact cathode composition based on La0.8Sr0.2MnO3±δ. It is shown that the initial powders obtained by the glycine-nitrate method according to the Pechini modification are preliminary prepared. The optimal grinding parameters have been determined. The sintering modes of the contact paste are selected, which are consistent with those for the sealing glass. An experimental SOFC assembly was made using a contact cathode paste. It is shown that the electrochemical characteristics of individual MEAs correspond to the declared ones and the specific power reaches 0.25W/cm2.This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071. Figure 1

Sr and Co Vapor-Phase Transport from LSCF Cathodes

A series of tests were performed to differentiate between surface diffusion and vapor-phase diffusion of chemical species from LSCF cathode material at typical sintering temperatures (up to 1100°C) in SOFC production. A GDC source substrate was printed with LSCF and separated by an air gap from a YSZ target substrate. Various geometries with long surface paths were employed to reduce the possibility of surface transport. Sr and Co were detected on the target substrates via energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), including spatially resolved XPS. These results support a vapor-phase transport mechanism for Sr and Co. Sintering conditions and barrier layer requirements may need to be revisited to prevent the formation of undesired strontium zirconate at cathode/electrolyte interface due to vapor-phase transport.

Identifying Descriptors to Predict the Sintering Temperature of Doped Llzo from First-Principles Simulations

The charge-discharge performance of a solid-state ceramic lithium battery is strongly affected by the interfacial contact between the electrodes and the solid-electrolyte. Post-annealing has shown promises to improve the physical contact between solid-electrolyte and Li metal anode, however this approach is far less effective at the interface with the cathode because very high ceramic processing temperatures are required to produce full densification at the interface. For example, typical sintering temperature of garnet LLZO is around 1100ºC, yet most cathode materials cannot survive a temperature above 900ºC. Lowering the LLZO sintering temperature to below 900ºC would enable new processing of more robust ceramic solid-state batteries. In this work, we use first-principles based simulation technique to explore how chemical modification of LLZO would affect its sintering behavior. We will determine a group of descriptors that can accurately and efficiently predict the sintering temperatures of doped LLZO compounds. We will further discuss the implication of doping towards Li-ion mobility in these doped LLZO compounds.

NH4Cl‐Modified ZnO for High‐Performance CsPbIBr2 Perovskite Solar Cells via Low‐Temperature Process

Recently, the thermally stable and facilely fabricated inorganic CsPbIBr2 perovskite solar cells (PSCs) have attracted tremendous attention where the electron transport layer (ETL) is vital. However, the typical sintering temperature for the widely used electron transport material, that is, TiO2, is more than 400 °C, elevating the cost and hindering the application. Due to high electron mobility and low fabrication temperature, ZnO becomes a desirable alternative for TiO2, as the ETL in CsPbIBr2 PSCs, albeit with low open‐circuit voltage (Voc). Herein, this work introduces a trace of NH4Cl to the sol–gel‐derived ZnO precursor to decrease the work function of the ZnO film, tune the surface morphology of the perovskite film, and thus suppress the density of trap states in the CsPbIBr2 films. Consequently, full‐coverage and pure‐phase CsPbIBr2 films consisting of micron‐size and high‐crystallinity grains are obtained. More importantly, for the optimal NH4Cl‐modified ZnO, a shining improvement in Voc from 1.08 to 1.27 V boosts the champion CsPbIBr2 PSCs to obtain a power conversion efficiency of 10.16%, which is the highest value reported among pure‐CsPbIBr2 PSCs under a low fabrication temperature of 160 °C. In addition, the NH4Cl‐modified ZnO ETL reduces the severe hysteresis and increases the device stability significantly.

Development of Advanced Nickelate-Based Oxygen Electrodes for Solid Oxide Cells

The present work deals with the development of lanthanide nickelate based oxygen electrodes (Ln2NiO4+ δ, with Ln = Nd, La or Pr) as the oxygen electrode for both solid oxide fuel cell (SOFC) and solid oxide electrolysis (SOEC) applications. The have been widely investigated as they present high oxygen diffusion parameters, making them attractive as SOFC oxygen electrodes. However, the main drawback of these nickelate phases is their reactivity with standard YSZ (yttria stabilized zirconia) or CGO (cerium gadolinium oxide) electrolytes, as typical sintering temperatures are usually higher than 1000 ºC in order to get strong adhesion at the electrode/electrolyte interface. Two strategies will be employed to avoid the undesired reactivity: the direct formation of the nickelate phase into YSZ scaffolds by infiltration and the development of active barrier layer.

Dramatic effects of chlorine addition on expanding synthesis conditions for fluorine-free metal–organic decomposition YBa2Cu3Oy films

The synthesis conditions of fluorine-free metal–organic decomposition (FF-MOD)-processed YBa2Cu3Oy (YBCO) films on buffered metallic substrates have been systematically investigated. Chlorine addition to the starting solution was found to be quite effective for expanding the synthesis conditions of highly c-axis-oriented YBCO films. YBCO films showing a high critical current, ∼100 A/cm (77 K, ∼0 T), were successfully obtained by sintering at 740 °C, which is ∼50 °C lower than the typical sintering temperature for FF-MOD-processed YBCO films. This strongly indicated that chlorine addition is promising for the development of long and homogeneous YBCO tapes even by sintering at a low temperature of ∼740 °C.

Influence of La2Zr2O7 Additive on Densification and Li+ Conductivity for Ta-Doped Li7La3Zr2O12 Garnet

A high-conductivity solid electrolyte, La2Zr2O7 (LZO) added to Li6.4La3Zr1.4Ta0.6O12 (LLZTO), was prepared via conventional solid-state reactions and sintered at 1100°C for 10 h, which is tens of Celsius degrees lower than the typical sintering temperature for LLZTO. The addition of LZO did not bring in any impurities. LZO acted as a sintering aid to densify the LLZTO from a relative density of 77% up to 90%, which was comparable to that of pure LLZTO sintered at 1200°C. The 6 wt.% LZO–LLZTO samples sintered at 1100°C and 1200°C exhibited a room-temperature conductivity of 1.92 × 10−4 S/cm and 5.84 × 10−4 S/cm, respectively, which were higher than that of pure LLZTO samples. Glass-like phases observed at grain boundaries in LZO–LLZTO ceramics indicated that LZO promoted the formation of the glass-like phases binding together LLZTO grains and thus leading to enhanced density and conductivity of LLZTO.

Cold Sintering Process of Composites: Bridging the Processing Temperature Gap of Ceramic and Polymer Materials

Co‐sintering ceramic and thermoplastic polymer composites in a single step with very high volume fractions of ceramics seems unlikely, given the vast differences in the typical sintering temperatures of ceramics versus polymers. These processing limitations are overcome with the introduction of a new sintering approach, namely “cold sintering process” (CSP). CSP utilizes a transient low temperature solvent, such as water or water with dissolved solutes in stoichiometric ratios consistent with the ceramic composition, to control the dissolution and precipitation of ceramics and effect densification between room temperature and ≈200 °C. Under these conditions, thermoplastic polymers and ceramic materials can be jointly formed into dense composites. Three diphasic composite examples are demonstrated to show the overall diversity of composite material design between organic and inorganic oxides, including the microwave dielectric Li2MoO4–(C2F4 ) n , electrolyte Li1.5Al0.5Ge1.5(PO4)3–(CH2CF2 ) x [CF2CF(CF3)] y , and semiconductor V2O5–poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate composites. Cold sintering is more general and shall have a major impact on the processing of composite materials for many different applications, mechanical, thermal, and electronic, to mention a few possibilities. CSP concepts open up new composite material design and device integration schemes, impacting a wide variety of applications.

ChemInform Abstract: Magnetic Properties of Nanostructured Spinel Ferrites

AbstractReview: 40 refs.

Magnetic Properties of Nanostructured Spinel Ferrites

Spinel ferrite nanoparticles (NPs) have raised interest due to their potential technological applications in fields as varied as high frequency electronic device components, soil remediation, and medical diagnosis and treatments. In this paper, we present a brief review of the magnetic properties of spinel ferrite NPs (Ni-Zn, Co, and magnetite) synthesized by the polyol method, in different degrees of aggregation, from monodisperse NPs, to clusters formed by tens to hundreds of NPs. We show that the approach to saturation can be modeled with a relationship derived from the Stoner-Wohlfarth model, both for ferrimagnetic and superparamagnetic NPs. We also present a review on the magnetic properties of spinel ferrites NPs consolidated using spark plasma sintering (SPS). This technique allows the sintering of NPs to densities 90% of the theoretical value at significantly lower temperatures and shorter times than the typical sintering processes, preserving the grain size within the nanometric range. The typical sintering temperatures are in the range 350°C-750°C, for times as short as 5 min. An interesting example is magnetite, which can be obtained as NPs by polyol, followed by SPS at 750°C, temperature that usually leads to the transformation to hematite. The Verwey transition is clearly observed as a large drop in the coercive field at ~120 K.

Microstructural, electrical, and mechanical characterization of Bi2Cu0.1V0.9O5.35 (BICUVOX) ceramics fabricated from co-precipitated precursor powders

Copper-doped bismuth vanadate (Bi2Cu0.1V0.9O5.35, BICUVOX) was synthesized by a co-precipitation process which resulted in a homogenous, fine-grained powder with an average particle size of ~0.45 μm. The consolidated BICUVOX powder was sintered at temperatures between 625 and 800 °C for 0–8 h in air. The correlation between the thermal processing schedule and the final microstructure were completed for all conditions through stereological analysis of the resultant cross-sectional scanning electron microscope images. From this work, the sintering schedule of 675 °C for 1 h resulted in acquiring a BICUVOX ceramic microstructure that displayed ~97 % relative density with an average grain size of ~1.29 μm. This processing condition was ~75–125 °C lower than typical sintering temperatures for the same density, and resulted in a final grain size that is ~5–10 μm smaller in size. The four-point conductivity testing of the BICUVOX ceramics in air showed values of ~0.003–0.007 and ~0.07–0.12 S/m at 300 °C and 500 °C, respectively, depending upon the thermal processing schedule. The average flexure strength of the same BICUVOX membrane was measured using a ring-on-ring configuration, and this measurement showed flexural strengths as high as 159.3 MPa. This strength is ~92 % greater than previously reported values for BICUVOX membranes.

Lanthanum oxide as a scavenging agent for zirconia electrolytes

The present work demonstrates that additions of lanthanum oxide can counter the negative grain boundary effects of relatively high silica contents in 8mol% yttria-stabilized zirconia (YSZ). This can be predicted by thermodynamic analysis, showing strong affinity between silica and lanthanum oxide at typical sintering temperatures. Microstructural analysis revealed the onset of La- and Si-rich precipitates, and impedance spectroscopy confirmed a positive impact on grain boundary conductivity. Gradual oversaturation of lanthana in YSZ with decreasing temperature allows one to extend these effects by heat treatment at intermediate temperatures. This procedure enhances the positive effects of additions of lanthana on the specific grain boundary conductivity, while minimizing the negative impact on bulk conductivity.

Grain boundary segregation and microwave dielectric properties of low loss Mg1·5Zn0·5SiO4 ceramics containing Bi2O3

Uncommon low loss Mg1·5Zn0·5SiO4 ceramics containing Bi2O3 were investigated by focusing on the roles of Bi2O3 on phase evolution and resultant microwave dielectric properties. While the primary goal of lowering sintering temperature can be easily assumed, some unexpected behaviours of the Bi2O3 containing materials are highlighted with experimental evidences concerning selective dissolution of Zn2SiO4 and grain boundary segregation of gradual Bi richer phases. These evidences are strongly dependent on the content of Bi2O3 and sintering temperature. As an optimal composition, Mg1·5Zn0·5SiO4 with 0·5 mol.-%Bi2O3 exhibited promising dielectric properties of a k value ∼6·8 and a Q×f value ∼23 300 at a sintering temperature of 1150°C, which is much lower than typical sintering temperature of 1450°C.

Synthesis of nanocrystalline samarium-doped CeO 2 (SDC) powders as a solid electrolyte by using a simple solvothermal route

Samarium-doped CeO 2 is a leading electrolyte for applications in solid oxide fuel cells (SOFCs), which requires a typical sintering temperature of 1400–1600 °C. In this work, fully dense CeO 2 ceramics doped with 10–20 at.% samarium have been fabricated by a simple polyol process. The XRD and SEM results show that a complete solid solution between CeO 2 and samarium was obtained at the sintering temperature of 1300 °C. And also the densification temperature is significantly lower than those (1400–1600 °C) reported for the SDC powders processed by modified sol–gel process and hydrothermal treatment. The resultant ceramics show the sizes of ultrafine grain are lower than 1 μm.

Effects of composition and frozen-in conditions on bulk and grain boundary conductivities of Yb 2Ti 2O 7-based materials

The present work provides a comprehensive interpretation of factors which affect cation and/or anion disordering in Yb 2Ti 2O 7-based materials, and their effects on transport properties. It also provides guidelines for further improvements of transport properties. Powder processing and thermal history may play major roles, especially when anti-site cation exchange is likely to occur at typical sintering temperatures, as confirmed by structural refinement. One found that the cooling rate may also determine changes in frozen-in conditions. Excessive sintering temperatures affect both the bulk and grain boundary properties of samples with composition Yb 2Ti 2O 7; this was ascribed to the formation of a Ti-rich amorphous phase, and corresponding excess of Yb in the bulk phase. Anti-site occupancy of B-site positions was found to affect ionic conductivity, as demonstrated for conditions that cause cation heterogeneities in Yb 2Ti 2O 7, and also by analysing conductivity data for compositions with excess of Yb. The conductivity data obtained for Yb 2 + x Ti 2 − x O 7 − d become less dependent on sample preparation, possibly because deliberate composition changes play a prevailing role, compared to intrinsic cationic and anionic disorders. Samples with slight excess of Ti retain prevailing ionic conductivity, which differs significantly from the effects of a typical donor additive on ionic and electronic conductivities.

Low temperature processing of dense samarium-doped CeO 2 ceramics: sintering and grain growth behaviors

Samarium-doped CeO 2 is a leading electrolyte for applications in solid oxide fuel cells (SOFCs), which requires a typical sintering temperature of 1400–1600 °C. By synthesizing reactive powders via carbonate precipitation, fully dense CeO 2 ceramics doped with 0–20 at.% of samarium have been fabricated in this work via pressureless sintering at a significantly lowered temperature of 1000 °C. The resultant ceramics show ultrafine grain sizes of ∼0.15–0.75 μm, depending upon the dopant concentration. Sintering studies indicated that samarium doping retards both densification and grain growth but increases the rate ratios of the two in the intermediate stage of sintering. Subsequent investigations on the grain growth in the fully densified ceramics also showed the suppressing effects of dopant, which tend to saturate at 10 at.% of samarium. The activation energy for grain growth increased from ∼186 to ∼254 kJ/mol by raising the samarium concentration from 5 to 20 at.%.