Thermochemistry of rare-earth orthophosphates

2001 ◽  
Vol 16 (9) ◽  
pp. 2623-2633 ◽  
Author(s):  
S. V. Ushakov ◽  
K. B. Helean ◽  
A. Navrotsky ◽  
L. A. Boatner
Keyword(s):  
Ionic Radius ◽  
Sodium Molybdate ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Lead Borate ◽  
Oxide Melt ◽  
Calorimetric Measurements ◽  
Formation Enthalpies ◽  
Tetravalent Actinide ◽  
Precipitation Formation

The enthalpies of formation for the compounds (RE3+)PO4, (where RE = Sc, Y, La–Nd, Sm–Lu) were determined by oxide-melt solution calorimetry. Calorimetric measurements were performed in a Calvet-type twin microcalorimeter in sodium molybdate (3Na2O · 4MoO3) and lead borate (2PbO · 2B2O3) solvents at 975 K. The experiments were carried out using both powdered single crystals grown by a flux technique and powders synthesized by precipitation. Formation enthalpies were derived from the drop-solution enthalpies for (RE)PO4, RE oxides, and P2O5. Enthalpies of formation for the (RE)PO4 compounds with respect to the oxides at 298 K become more negative with increasing RE3+ ionic radius; i.e., in going from ScPO4 (−209.8 ± 1.0 kJ/mol), to LuPO4 (−263.9 ± 1.9 kJ/mol), to LaPO4 (−321.4 ± 1.6 kJ/mol). From structural considerations, a similar trend is expected for the isostructural RE vanadates and arsenates, as well as for the tetravalent actinide orthosilicates.

scholarly journals Enthalpies of formation of lanthanide oxyapatite phases

2001 ◽  
Vol 16 (10) ◽  
pp. 2780-2783 ◽  
Author(s):  
A. S. Risbud ◽  
K. B. Helean ◽  
M. C. Wilding ◽  
P. Lu ◽  
A. Navrotsky
Keyword(s):  
Structural Formula ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Enthalpies Of Solution ◽  
Thermodynamic Cycles ◽  
Oxide Melt ◽  
Formation Enthalpies ◽  
High Temperature Oxide ◽  
Standard Enthalpies Of Formation ◽  
Temperature Oxide

A family of lanthanide silicates adopts an oxyapatitelike structure with structural formula Ln9.33 0.67(SiO4)6O2 (Ln = La, Sm, Nd, Gd,   = vacancy). The enthalpies of solution, ΔHS, for these materials and their corresponding binary oxides were determined by high-temperature oxide melt solution calorimetry using molten 2PbO B2O3 at 1078 K. These data were used to complete thermodynamic cycles to calculate enthalpies of formation from the oxides, ΔH0 f-oxides (kJ/mol): La9.33 0.67(SiO4)6O2 = 776.3 ± 17.9, Nd9.33 0.67(SiO4)6O2 = 760.4 ± 31.9, Sm9.33 0.67(SiO4)6O2 = 590.3 ± 18.6, and Gd9.33 0.67(SiO4)6O2 = 446.9 ± 21.9. Reference data were used to calculate the standard enthalpies of formation from the elements, ΔH0 f (kJ/mol): La9.33 0.67(SiO4)6O2 = 14611.0 ± 19.4, Nd9.33 0.67(SiO4)6O2 = 14661.5 ± 32.2, Sm9.33 0.67(SiO4)6O2 = -14561.7 ±; 20.8, and Gd9.33 0.67(SiO4)6O2 = -14402.7 ± 28.2. The formation enthalpies become more endothermic as the ionic radius of the lanthanide ion decreases.

scholarly journals Thermodynamics of Molybdenum Trioxide (MoO3) Encapsulated in Zeolite Y

2021 ◽  
Author(s):  
Xianghui Zhang ◽  
Andrew Strzelecki ◽  
Cody Cockreham ◽  
Vitaliy Goncharov ◽  
Houqian Li ◽  
...  
Keyword(s):  
Molybdenum Trioxide ◽  
Zeolite Y ◽  
Formation Enthalpy ◽  
Solution Calorimetry ◽  
Metal Species ◽  
Enthalpies Of Formation ◽  
Host Interactions ◽  
Oxide Melt ◽  
High Temperature Oxide ◽  
Temperature Oxide

Zeolites with encapsulated transition metal species are extensively applied in the chemical industry as heterogenous catalysts for favorable kinetic pathways. To elucidate the energetic insights into formation of subnano-sized molybdenum trioxide (MoO) encapsulated/confined in zeolite Y (FAU) from constituent oxides, we performed a systematic experimental thermodynamic study using high temperature oxide melt solution calorimetry as the major tool. Specifically, the formation enthalpy of each MoO/FAU is less endothermic than corresponding zeolite Y, suggesting enhanced thermodynamic stability. As Si/Al ratio increases, the enthalpies of formation of MoO/FAU with identical loading (5 Mo-wt%) tend to be less endothermic, ranging from 61.1 ± 1.8 (Si/Al = 2.9) to 32.8 ± 1.4 kJ/mol TO (Si/Al = 45.6). Coupled with spectroscopic, structural and morphological characterizations, we revealed intricate energetics of MoO – zeolite Y guest – host interactions likely determined by the subtle redox and/or phase evolutions of encapsulated MoO.

Thermochemistry of lanthanum zirconate pyrochlore

2009 ◽  
Vol 24 (11) ◽  
pp. 3350-3357 ◽  
Author(s):  
A.V. Radha ◽  
Sergey V. Ushakov ◽  
Alexandra Navrotsky
Keyword(s):  
Melting Point ◽  
Enthalpy Of Formation ◽  
Sodium Molybdate ◽  
Solution Calorimetry ◽  
Standard Enthalpy Of Formation ◽  
Lanthanum Zirconate ◽  
Oxide Melt ◽  
High Temperature Oxide ◽  
Temperature Oxide ◽  
The Enthalpy Of Formation

A thermodynamic study was carried out to resolve discrepancies in the enthalpy of formation and related parameters for lanthanum zirconate pyrochlore. The homogeneity field for single phase pyrochlore formation was determined to be ∼33–35 mol% La2O3 at 1500 °C. High-temperature oxide melt drop solution calorimetry was performed in sodium molybdate and lead borate solvents on three compositions ranging from La1.98Zr2.01O7 to La2.07Zr1.95O7. The enthalpy of formation from oxides at 25 °C, ΔH0f,ox, for stoichiometric lanthanum zirconate pyrochlore is −107.3 ± 5.1 kJ/mol, and the standard enthalpy of formation from elements, ΔH0f,el, is −4102.2 ± 6.0 kJ/mol. La2Zr2O7 pyrochlore was found by differential thermal analysis to be stable up to its melting point. The melting point and the fusion enthalpy of La2Zr2O7 pyrochlore were measured as 2295 ± 10 °C and ∼350 kJ/mol, respectively.

Enthalpy of Formation of Yttria-Doped Ceria

2005 ◽  
Vol 20 (1) ◽  
pp. 144-150 ◽  
Author(s):  
Weiqun Chen ◽  
Theresa A. Lee ◽  
Alexandra Navrotsky
Keyword(s):  
Enthalpy Of Formation ◽  
Nearest Neighbor ◽  
Linear Trend ◽  
Sol Gel ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Oxide Melt ◽  
Linear Behavior ◽  
Transition Enthalpy ◽  
Fluorite Type

Solid solutions (1 − x)CeO2 − xYO1.5 (0 ≤ x ≤ 0.36) were prepared by coprecipitation and sol-gel methods. Their enthalpy of formation relative to the end-members, fluorite-type cubic CeO2 and C-type YO1.5 was determined by oxide melt solution calorimetry. The enthalpy of drop solution shows a roughly linear trend with composition. Extrapolation to x = 1 gives the transition enthalpy of C-type to cubic fluorite YO1.5 as 22.2 ± 6.7 kJ/mol. This linear behavior is in contrast to the strong curvature seen in the ZrO2 − YO1.5 and HfO2 − YO1.5 systems. The slightly positive enthalpy of formation of CeO2 − YO1.5 is strikingly different from the strongly negative enthalpies of formation of ZrO2 − YO1.5 and HfO2 − YO1.5. The thermodynamics of CeO2 − YO1.5 is analyzed in terms of defect association and oxygen vacancy distribution. Specifically, the association of oxygen vacancies with the tetravalent cations in the zirconia and hafnia systems, in contrast to the preference of vacancies for nearest neighbor yttrium sites in the ceria systems, may explain the different energetics.

Formation Enthalpies of Tetravalent Lanthanide Perovskites by High Temperature Oxide Melt Solution Calorimetry

2002 ◽  
Vol 718 ◽  
Author(s):  
S. V. Ushakov ◽  
J. Cheng ◽  
A. Navrotsky ◽  
J. R. Wu ◽  
S. M. Haile
Keyword(s):  
High Temperature ◽  
Rietveld Method ◽  
Thermal Analyses ◽  
Formation Enthalpy ◽  
Solution Calorimetry ◽  
Cell Parameters ◽  
Oxide Melt ◽  
Formation Enthalpies ◽  
High Temperature Oxide ◽  
Temperature Oxide

AbstractHigh-temperature oxide melt solution calorimetry was used to measure formation enthalpies for several compositions of perovskites of nominal stoichiometry BaPrO3 and BaCeO3. Samples were synthesized from chemical solution methods followed by calcination at 1100-1300°C. PrO2 was synthesized by oxidation of Pr6O11 in an oxygen flow at 280°C. The samples were characterized by microprobe, thermogravimetric and differential thermal analyses. Cell parameters were refined by the Rietveld method. Barium excess in the samples with respect to ideal stoichiometry was detected. Drop solution enthalpies were measured in a Calvet type twin microcalorimeter, using 3Na2O·4MoO3 solvent at 702°C. Preliminary values of the formation enthalpy of BaPrO3 and BaCeO3 from oxides were -70 ±10 kJ/mol and -51 ±10 kJ/mol, respectively. They fall on the normal trend of energetics versus Goldschmidt tolerance factor and do not show any special stabilization of BaPrO3 relative to other MLnO3 perovskites.

Thermochemistry of Rare Earth Perovskites

MRS Advances ◽  
2016 ◽  
Vol 1 (38) ◽  
pp. 2695-2700 ◽  
Author(s):  
Dawei Feng ◽  
Alexandra Navrotsky
Keyword(s):  
Rare Earth ◽  
Solid Solutions ◽  
Solution Calorimetry ◽  
Sodium Content ◽  
Enthalpies Of Formation ◽  
Oxide Melt ◽  
High Temperature Oxide ◽  
Temperature Oxide ◽  
Image Position ◽  
Light Rare Earth Elements

AbstractThe rare earth (RE) mineral loparite with the chemical composition (RE, Na, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3 is the principal ore of the light rare earth elements (LREE) as well as niobium and tantalum. The enthalpies of formation of RE0.67-xNa3xTiO3 (RE = La, Ce) and Ca1-2xNaxLaxTiO3 from oxides and elements of lanthanum and cerium perovskites and their solid solutions have been obtained using high temperature oxide melt solution calorimetry. RE0.67-xNa3xTiO3 (RE = La, Ce) perovskites become more stable relative to oxide components as sodium content increases. Na0.5Ce0.5TiO3 and Na0.5La0.5TiO3 can be considered stable endmembers in natural loparite minerals. For perovskite solid solutions Ca1-2xNaxLaxTiO3, the enthalpies of formation from the constituent oxides $\Delta {\rm{H}}_{{\rm{f}},\,{\rm{ox}}}^^\circ$ become more exothermic with increasing Na+La content, suggesting a stabilizing effect of the substitution 2Ca2+ → Na+ + La3+ on the perovskite structure. The trend of increasing thermodynamic stability with decreasing structural distortion is similar to that seen in many other ABO3 perovskites.

Enthalpies of formation of LaBO3perovskites (B = Al, Ga, Sc, and In)

2003 ◽  
Vol 18 (10) ◽  
pp. 2501-2508 ◽  
Author(s):  
Jihong Cheng ◽  
Alexandra Navrotsky
Keyword(s):  
High Temperature ◽  
Enthalpy Of Formation ◽  
Solution Calorimetry ◽  
Tolerance Factor ◽  
Enthalpies Of Formation ◽  
Oxide Melt ◽  
High Temperature Oxide ◽  
Temperature Oxide ◽  
First Time ◽  
The Enthalpy Of Formation

Enthalpies of formation from constituent oxides and elements at 298 K were determined by high-temperature oxide melt solution calorimetry for a group of technologically important perovskites LaBO3(B = La, Ga, Sc, and In). Enthalpies of formation from oxides of LaAlO3and LaGaO3are −69.61 ± 3.23 kJ/mol and −52.39 ± 1.99 kJ/mol, respectively. The data were consistent with literature values obtained using other methods. The enthalpies of formation of LaScO3and LaInO3from oxides were reported for the first time as −38.64 ± 2.30 kJ/mol and −23.99 ± 2.31 kJ/mol, respectively. As seen for other perovskites, as the tolerance factor deviates more from unity (in the order Al, Ga, Sc, In), the enthalpy of formation from oxides becomes less exothermic, indicating a less stable structure with respect to the constituent oxides.

scholarly journals Thermodynamics of Molybdenum Trioxide (MoO3) Encapsulated in Zeolite Y

2021 ◽  
Author(s):  
Xianghui Zhang ◽  
Vitaliy Goncharov ◽  
Cody Cockreham ◽  
Houqian Li ◽  
Junming Sun ◽  
...  
Keyword(s):  
Molybdenum Trioxide ◽  
Zeolite Y ◽  
Formation Enthalpy ◽  
Solution Calorimetry ◽  
Catalytic Performance ◽  
Metal Species ◽  
Enthalpies Of Formation ◽  
Host Interactions ◽  
Oxide Melt ◽  
High Temperature Oxide

Zeolites with encapsulated transition metal species are extensively applied in the chemical industry as heterogenous catalysts for favorable kinetic pathways. To elucidate the energetic insights into formation of subnano-sized molybdenum trioxide (MoO3) encapsulated/confined in zeolite Y (FAU) from constituent oxides, we performed a systematic experimental thermodynamic study using high temperature oxide melt solution calorimetry as the major tool. Specifically, the formation enthalpy of each MoO3/FAU is less endothermic than corresponding zeolite Y, suggesting enhanced thermodynamic stability. As Si/Al ratio increases, the enthalpies of formation of MoO3/FAU with identical MoO3 loading tends to be less endothermic, ranging from 61.1 ± 1.8 (Si/Al = 2.9) to 32.8 ± 1.4 kJ/mol TO2 (Si/Al = 45.6). Coupled with spectroscopic, structural and morphological characterizations, and catalytic performance tests, we revealed intricate energetics of MoO3 – zeolite Y guest – host interactions and catalytic performance governed by the phase evolutions of encapsulated MoO3.

Octahedral microporous phases Na2Nb2−xTixO6−x(OH)x·H2O and their related perovskites: Crystal chemistry, energetics, and stability relations

2005 ◽  
Vol 20 (3) ◽  
pp. 618-627 ◽  
Author(s):  
Hongwu Xu ◽  
Alexandra Navrotsky ◽  
May D. Nyman ◽  
Tina M. Nenoff
Keyword(s):  
Crystal Chemistry ◽  
Phase Stability ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Dehydration Reaction ◽  
Calorimetric Data ◽  
Synthesis Conditions ◽  
Formation Enthalpies

A family of microporous phases with compositions Na2Nb2−xTixO6−x(OH)x⋅H2O (0 ≤ x ≤ 0.4) transform to Na2Nb2−xTixO6−0.5x perovskites upon heating. In this study, we have measured the enthalpies of formation of the microporous phases and their corresponding perovskites from the constituent oxides and from the elements by drop solution calorimetry in 3Na2O·4MoO3 solvent at 974 K. As Ti/Nb increases, the enthalpies of formation for the microporous phases become less exothermic up to x = ∼0.2 but then more exothermic thereafter. In contrast, the formation enthalpies for the corresponding perovskites become less exothermic across the series. The energetic disparity between the two series can be attributed to their different mechanisms of ionic substitutions: Nb5+ + O2− → Ti4+ + OH− for the microporous phases and Nb5+ → Ti4+ + 0.5VO.. for the perovskites. From the calorimetric data for the two series, the enthalpies of the dehydration reaction, Na2Nb2−xTixO6−x(OH)x⋅H2O → Na2Nb2−xTixO6−0.5x + H2O, have been derived, and their implications for phase stability at the synthesis conditions are discussed.

Energetics of rare-earth-doped hafnia

2007 ◽  
Vol 22 (4) ◽  
pp. 876-885 ◽  
Author(s):  
Petra Simoncic ◽  
Alexandra Navrotsky
Keyword(s):  
Rare Earth ◽  
Solid Solutions ◽  
Energy Difference ◽  
Solution Calorimetry ◽  
Interaction Parameters ◽  
Enthalpies Of Formation ◽  
Amorphous Phases ◽  
Oxide Melt ◽  
Local Structures ◽  
End Members

The enthalpies of formation of rare-earth (RE)-doped Hf1−xRExO2−x/2 solid solutions (RE = Sm, Gd, Dy, Yb; x = 0.25 to 0.62) with respect to the oxide end members, monoclinic HfO2 and C-type REO1.5, were determined using oxide melt solution calorimetry. The enthalpies of formation fit a function quadratic in composition. The strongly negative interaction parameters in all solid solutions confirm a strong tendency for short-range order. Though strongly negative for all systems, the interaction parameters become less negative with increasing ionic potential (decreasing RE radius). Crystallization energetics were investigated for amorphous coprecipitation products with x = 0.4. The energy difference between the crystalline (fluorite and pyrochlore) and amorphous phases decreases with decreasing dopant radius. This suggests that systems doped with small RE ions have more similar local structures in the fluorite and amorphous phases. These observations may result in a smaller kinetic barrier to recrystallization and account for the greater radiation resistance of materials with smaller RE cations.

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