Thermochemistry of Substituted Perovskites in the NaTixNb1-xO3-0.5x System

2002 ◽  
Vol 718 ◽  
Author(s):  
Hongwu Xu ◽  
Alexandra Navrotsky ◽  
M. Lou Balmer ◽  
Yali Su
Keyword(s):  
Perovskite Structure ◽  
Sol Gel ◽  
Rietveld Analysis ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Charge Imbalance ◽  
Cell Parameters ◽  
Formation Enthalpies ◽  
First Time ◽  
Linear Manner

AbstractA suite of perovskite phases with the compositions NaTixNb1-xO3-0.5x, 0 ≤ x ≤ 0.2, has been synthesized for the first time using the sol-gel method. Rietveld analysis of powder XRD data reveals that with increasing Ti content, the orthorhombic perovskite structure becomes more cubic-like, as evidenced by the smaller differences among its three cell parameters. Enthalpies of formation of the synthesized phases from the constituent oxides and from the elements have been determined by drop solution calorimetry into molten 3Na2O·4MoO3 solvent at 974 K. As Ti4+ substitutes for Nb5+, the formation enthalpies become less exothermic in a nearly linear manner. This behavior suggests that the Ti→Nb substitution destabilizes the perovskite structure, presumably because of the concomitant occurrence of O2- vacancies, which compensate the charge imbalance between Ti4+ and Nb5+ in the structure.

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.

scholarly journals Microwave-Employed Sol–Gel Synthesis of Scheelite-Type Microcrystalline AgGd(MoO4)2:Yb3+/Ho3+ Upconversion Yellow Phosphors and Their Spectroscopic Properties

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1000
Author(s):  
Chang Sung Lim ◽  
Aleksandr Aleksandrovsky ◽  
Victor Atuchin ◽  
Maxim Molokeev ◽  
Aleksandr Oreshonkov
Keyword(s):  
Sol Gel ◽  
Green Emission ◽  
Spectroscopic Properties ◽  
Rietveld Analysis ◽  
Optimal Number ◽  
Concentration Effects ◽  
Characteristic Energy ◽  
Structure Variation ◽  
Cell Parameters ◽  
Level Increase

AgGd(MoO4)2:Ho3+/Yb3+ double molybdates with five concentrations of Ho3+ and Yb3+ were synthesized by the microwave employed sol–gel based process (MES), and the crystal structure variation, concentration effects, and spectroscopic characteristics were investigated. The crystal structures of AgGd1−x−yHoxYby(MoO4)2 (x = 0, 0.05; y = 0, 0.35, 0.4, 0.45, 0.5)at room temperature were determined in space group I41/a by Rietveld analysis. Pure AgGd(MoO4)2 has a scheelite-type structure with mixed occupations of (Ag,Gd) sites and cell parameters a = 5.24782 (11) and c = 11.5107 (3) Å, V = 317.002 (17) Å3, Z = 4. In doped samples, the sites are occupied by a mixture of (Ag,Gd,Ho,Yb) ions, which provides a linear cell volume decrease with the doping level increase. Under the excitation at 980 nm, AGM:0.05Ho,yYb phosphors exhibited a yellowish green emission composed of red and green emission bands according to the strong transitions 5F5 → 5I8 and 5S2/5F4 → 5I8 of Ho3+ ions. The evaluated photoluminescence and Raman spectroscopic results were discussed in detail. The upconversion intensity behavior dependent on the Yb/Ho ratio is explained in terms of the optimal number of Yb3+ ions at the characteristic energy transfer distance around the Ho3+ ion.

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 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.

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.

scholarly journals Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1-xCaGd0.5Ho0.05Yb0.45(MoO4)3 Scheelite-Type Upconversion Phosphors

Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7357
Author(s):  
Chang-Sung Lim ◽  
Aleksandr Aleksandrovsky ◽  
Maxim Molokeev ◽  
Aleksandr Oreshonkov ◽  
Victor Atuchin
Keyword(s):  
Transition Probabilities ◽  
Sol Gel ◽  
Green Emission ◽  
Local Symmetry ◽  
Rietveld Analysis ◽  
Cell Parameters ◽  
Li Doping ◽  
The Individual ◽  
Li Content ◽  
Triple Molybdates

A set of new triple molybdates, LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45, was successfully manufactured by the microwave-accompanied sol–gel-based process (MAS). Yellow molybdate phosphors LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45 with variation of the LixNa1-x (x = 0, 0.05, 0.1, 0.2, 0.3) ratio under constant doping amounts of Ho3+ = 0.05 and Yb3+ = 0.45 were obtained, and the effect of Li+ on their spectroscopic features was investigated. The crystal structures of LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) at room temperature were determined in space group I41/a by Rietveld analysis. Pure NaCaGd0.5Ho0.05Yb0.45(MoO4)3 has a scheelite-type structure with cell parameters a = 5.2077 (2) and c = 11.3657 (5) Å, V = 308.24 (3) Å3, Z = 4. In Li-doped samples, big cation sites are occupied by a mixture of (Li,Na,Gd,Ho,Yb) ions, and this provides a linear cell volume decrease with increasing Li doping level. The evaluated upconversion (UC) behavior and Raman spectroscopic results of the phosphors are discussed in detail. Under excitation at 980 nm, the phosphors provide yellow color emission based on the 5S2/5F4 → 5I8 green emission and the 5F5 → 5I8 red emission. The incorporated Li+ ions gave rise to local symmetry distortion (LSD) around the cations in the substituted crystalline structure by the Ho3+ and Yb3+ ions, and they further affected the UC transition probabilities in triple molybdates LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45. The complex UC intensity dependence on the Li content is explained by the specificity of unit cell distortion in a disordered large ion system within the scheelite crystal structure. The Raman spectra of LixNa1-xCaGd0.5(MoO4)3 doped with Ho3+ and Yb3+ ions were totally superimposed with the luminescence signal of Ho3+ ions in the range of Mo–O stretching vibrations, and increasing the Li+ content resulted in a change in the Ho3+ multiplet intensity. The individual chromaticity points (ICP) for the LiNaCaGd(MoO4)3:Ho3+,Yb3+ phosphors correspond to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.

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.

Fluorite and Pyrochlore Phases in the HfO2 -La2O3 -Gd2O3 Systems: Characterization and Calorimetric Study of Samples Quenched From Melts Formed by Laser Heating and Aerodynamic Levitation

2008 ◽  
Vol 1122 ◽  
Author(s):  
Sergey V. Ushakov ◽  
Alexandra Navrotsky ◽  
Jean A. Tangeman
Keyword(s):  
Thin Films ◽  
Solution Calorimetry ◽  
Enthalpies Of Formation ◽  
Fluorite Phase ◽  
Calorimetric Study ◽  
Amorphous Precursor ◽  
Cell Parameters ◽  
Fluorite Type ◽  
Temperature Solution ◽  
Damaged Materials

AbstractNew experimental results on pyrochlore and defect fluorite phases in HfO2-La2O3 and HfO2-Gd2O3 systems are summarized. Fluorite Hf0.5Gd0.5O1.75 was formed by containerless melting and quenching. Melts with 25-65 mol% La2O3 did not produce any fluorite-type phases, but pyrochlores with cell parameters 10.74 to 10.86 Å. The fluorite phase of Hf0.5La0.5O1.75 can be formed on crystallization of an amorphous precursor from aqueous precipitation. Both La- and Gd- fluorite phases transform to ordered pyrochlore on annealing at 1450 °C. The enthalpies of formation from oxides are −107 ±5 kJ/mol for Hf2La2O7 and −49 ±5 kJ/mol for Hf2Gd2O7 as measured by high-temperature solution calorimetry. Further experiments are needed to elucidate the nature of stabilization of fluorite phase in thin films and powders. Occurrence of disordered phases in thin films, nanoparticles and radiation damaged materials is discussed.

scholarly journals Synthesis of novel adsorbent based on tetrasulfide-functionalized fibrous silica KCC-1 for removal of Hg(II) cations

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Azam Marjani ◽  
Reza Khan Mohammadi
Keyword(s):  
Effective Interaction ◽  
Sol Gel ◽  
Aqueous Media ◽  
Synthesis Method ◽  
Mercury Ions ◽  
Toxic Heavy Metals ◽  
Uptake Capacity ◽  
Hydrothermal Preparation ◽  
Ultrasonic Assisted ◽  
First Time

AbstractHg(II) has been identified to be one of the extremely toxic heavy metals because of its hazardous effects and this fact that it is even more hazardous to animals than other pollutants such as Ag, Au, Cd, Ni, Pb, Co, Cu, and Zn. Accordingly, for the first time, tetrasulfide-functionalized fibrous silica KCC-1 (TS-KCC-1) spheres were synthesized by a facile, conventional ultrasonic-assisted, sol–gel-hydrothermal preparation approach to adsorb Hg(II) from aqueous solution. Tetrasulfide groups (–S–S–S–S–) were chosen as binding sites due to the strong and effective interaction of mercury ions (Hg(II)) with sulfur atoms. Hg(II) uptake onto TS-KCC-1 in a batch system has been carried out. Isotherm and kinetic results showed a very agreed agreement with Langmuir and pseudo-first-order models, respectively, with a Langmuir maximum uptake capacity of 132.55 mg g–1 (volume of the solution = 20.0 mL; adsorbent dose = 5.0 mg; pH = 5.0; temperature: 198 K; contact time = 40 min; shaking speed = 180 rpm). TS-KCC-1was shown to be a promising functional nanoporous material for the uptake of Hg(II) cations from aqueous media. To the best of our knowledge, there has been no report on the uptake of toxic Hg(II) cations by tetrasulfide-functionalized KCC-1 prepared by a conventional ultrasonic-assisted sol–gel-hydrothermal synthesis method.

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