High-temperature Drop Solution Research Articles

Calorimetric Studies on Chemically Delithiated LiNi0.4Mn0.4Co0.2O2: Investigation of Phase Transition, Gas Evolution and Enthalpy of Formation

Li1.11(Ni0.4Mn0.4Co0.2)O2 powders were chemically delithiated by (NH4)2S2O8 oxidizer to obtain Lix(Ni0.4Mn0.4Co0.2)O2 powders. The thermal behavior of two delithiated specimens, Li0.76Ni0.41Mn0.42Co0.17O2.10 and Li0.48Ni0.38Mn0.46Co0.16O2.07, was studied compared to the pristine specimen. Phase transitions at elevated temperatures were investigated by simultaneous thermal analysis (STA) and the gas evolution accompanying the phase transitions was analyzed by mass spectroscopy and an oxygen detector. The enthalpy of two delithiated samples and a pristine specimen were measured by a high temperature drop solution calorimeter. Based on these results, the enthalpies of formation were calculated.

Thermodynamic properties of selected glasses in the CaO–Al2O3–TiO2 system

The thermodynamic properties of a Ca12Al14O33 (C12A7) binary glass and the impact of titania additions (+5 and 7 wt%) were studied for the first time using three different calorimetric techniques: low-temperature adiabatic, high-temperature drop solution and transposed temperature drop calorimetry. The enthalpy of formation from oxides at 298.15 K of the Ca12Al14O33 and Ca12Al14O33+7 wt% TiO2 glass samples (16.0±1.8 and 14.5±2.4 kJ/mol, respectively) and the enthalpy of dissolution of TiO2 (rut) at 1073.15 K were obtained by drop solution calorimetry in a 2PbO–B2O3 solvent. A close value (11.9±2.3 kJ/mol) was obtained for the same C12A7 glass by transposed temperature drop calorimetry. The investigation of the impact of TiO2 additions on the thermodynamic properties of glasses shows that there is no influence on heat capacity of C12A7 up to 7 wt% of TiO2. In contrast, a negative deviation of the enthalpy of formation from oxides at 298.15 K from the ideal-mixing straight line was observed.

A Novel Family of Np(VI) Oxysalts: Crystal Structures, Calorimetry, Thermal Behavior, and Comparison with U(VI) Compounds

Phase formation in the mixed sulfate–selenate Np(VI)-bearing aqueous system has been investigated. The obtained crystalline compounds, Cs2[(NpO2)2(TO4)3] (T = S, Se), crystallize in the tetragonal system, space group P421m, with a = 9.5737(3)–9.817(3) A, c = 8.0824(4)–8.111(3) A, and V = 740.79(6)–781.8(6) A3, and have been chemically characterized. Single-crystal X-ray diffraction experiments at various temperatures were used to define the thermal behavior of the crystal structures relative to the S/Se ratio. The thermal behavior of mixed sulfate–selenate and pure selenate compounds is anisotropic, with the highest thermal expansion in the direction perpendicular to the sheets of Np-bearing polyhedra, while the structure of the pure sulfate compound experiences almost isotropic thermal expansion with slightly higher expansion within the layer, which is explained by the influence of stronger Cs–O bonding. High-temperature drop solution calorimetry was used to derive the enthalpies of formation of the Cs+...

Thermodynamics and Stability of Rhabdophanes, Hydrated Rare Earth Phosphates REPO4 · n H2O.

Rare earth phosphates comprise a large family of compounds proposed as possible nuclear waste disposal forms. We report structural and thermodynamic properties of a series of rare earth rhabdophanes and monazites. The water content of the rhabdophanes, including both adsorbed and structural water, decreases linearly with increase in ionic radius of the rare earth. The energetics of the transformation of rhabdophane to monazite plus water and the enthalpy of formation of rhabdophane from the constituent oxides was determined by high temperature drop solution calorimetry. The former varies linearly with the ionic radius of the lanthanide, except for cerium. By combining the enthalpy of formation determined by high temperature drop solution calorimetry and the free energy of formation determined previously by solubility experiments, a complete set of thermodynamic data was derived for the rhabdophanes. They are thermodynamically metastable with respect to the corresponding monazites plus water at all temperatures under ambient pressure conditions. This conclusion strengthens the case for monazites being an excellent nuclear waste form.

Charge Density Influence on Enthalpy of Formation of Uranyl Peroxide Cage Cluster Salts.

More than 60 unique uranyl peroxide cage clusters have been reported that contain as many as 124 uranyl ions and that have overall diameters extending to 4 nm. They self-assemble in water under ambient conditions, are models for understanding structure-size-property relations as well as testing computational models for actinides, and have potential applications in nuclear fuel cycles. High-temperature drop solution calorimetry has been used to derive the enthalpies of formation of the salts of seven topologically diverse uranyl peroxide cage clusters containing from 22 to 28 uranyl ions that are bridged by various combinations of peroxide, pyrophosphate, and phosphite. The enthalpies of formation of these seven salts, as well as three salts of other uranyl peroxide clusters reported earlier, are dominated by the interactions of the alkali countercations with the clusters. There is an approximately linear relationship between the enthalpies of formation of the cluster salts and the charge density of the corresponding uranyl peroxide cluster, wherein salts containing clusters with higher charge densities have more negative enthalpies of formation.

Thermodynamic investigation of uranyl vanadate minerals: Implications for structural stability

Understanding the crystal chemistry, materials properties, and thermodynamics of uranyl minerals and their synthetic analogs is an essential step for predicting and controlling the long-term environmental behavior of uranium. Uranyl vanadate minerals are relatively insoluble and widely disseminated within U ore deposits and mine and mill tailings. Pure uranyl vanadate mineral analogs were synthesized for investigation using high-temperature drop solution calorimetry. Calculated standard-state enthalpies of formation were found to be −4928.52 ± 13.90, −5748.81 ± 13.59, and −6402.88 ± 21.01, kJ/mol for carnotite, curienite, and francevillite, respectively. Enthalpies of formation from binary oxides for uranyl vanadate minerals exhibit a positive linear correlation as a function of the acidity of oxides. Normalized charge deficiency per anion (NCDA) is presented to relate bonding requirements of the structural units and interstitial complexes. An exponential correlation was observed between NCDA and energetic stability (enthalpy of formation from binary oxides) for the studied minerals. Additionally, NCDA and oxide acidity exhibit an exponential correlation where decreasing oxide acidity results in an exponential decrease in NCDA. The number of occurrences of uranyl vanadate mineral species are found to correlate with both enthalpy of formation from oxides and NCDA.

Thermochemistry, Morphology, and Optical Characterization of Germanium Allotropes

A thermochemical study of three germanium allotropes by differential scanning calorimetry (DSC) and oxidative high-temperature drop solution calorimetry with sodium molybdate as the solvent is described. Two allotropes, microcrystalline allo-Ge (m-allo-Ge) and 4H-Ge, have been prepared by topotactic deintercalation of Li7Ge12 with methanol (m-allo-Ge) and subsequent annealing at 250 °C (4H-Ge). Transition enthalpies determined by differential scanning calorimetry amount to 4.96(5) ± 0.59 kJ/mol (m-allo-Ge) and 1.46 ± 0.55 kJ/mol (4H-Ge). From high-temperature drop solution calorimetry, they are energetically less stable by 2.71 ± 2.79 kJ/mol (m-allo-Ge) and 5.76 ± 5.12 kJ/mol (4H-Ge) than α-Ge, which is the stable form of germanium under ambient conditions. These data are in agreement with DSC, as well as with the previous quantum chemical calculations. The morphology of the m-allo-Ge and 4H-Ge crystallites was investigated by a combination of scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Even though the crystal structures of m-allo-Ge and 4H-Ge cannot be considered as truly layered, these phases retain the crystalline morphology of the layered precursor Li7Ge12. Investigation by diffuse reflectance infrared Fourier transform spectroscopy and UV–vis diffuse reflectance measurements reveal band gaps in agreement with quantum chemical calculations.

Fluorite-pyrochlore transformation in Eu2Zr2O7—direct calorimetric measurement of phase transition, formation and surface enthalpies

The energetics of the order-disorder phase transformation in the binary oxide system, Eu2O3–ZrO2, is studied by powder X-ray diffraction and high temperature drop solution calorimetry. The nanocrystalline defect fluorite phase of Eu2Zr2O7 is synthesized on crystallization of an amorphous precursor from aqueous precipitation. The defect fluorite transforms to an ordered pyrochlore above 1200 °C. Aerodynamic levitation combined with laser heating is used to prepare coarse defect fluorite, which is otherwise impossible by conventional synthesis techniques. Formation enthalpies from oxides are −62.4 ± 2.6 and −24.6 ± 3.7 kJ mol−1 for the pyrochlore and defect fluorite phase, respectively. The transformation enthalpy from pyrochlore to defect flourite in the coarse sample is 37.8 ± 3.1 kJ mol−1 at 25 °C. The enthalpy of water vapor adsorption on the surface of the nanocrystalline defect fluorite Eu2Zr2O7 is −75 ± 2.5 kJ mol−1 H2O for coverage of 9.5 ± 0.8 H2O/nm2. The calculated surface enthalpies for the anhydrous and hydrous surfaces of defect fluorite Eu2Zr2O7 are 1.47 ± 0.13 and 1.01 ± 0.15 J m−2, respectively.

TiO2Stability Landscape: Polymorphism, Surface Energy, and Bound Water Energetics

The energetics of pure-phase rutile nanorods and spherical anatase nanoparticles have been studied by high-temperature drop solution calorimetry in 3Na2O·4MoO3 solvent at 975 K and water adsorption calorimetry in a wide range of particle sizes (surface area) from 6 to 40 nm (5−270 m2/g). The calorimetric surface enthalpies for rutile and anatase, calculated as 2.22 ± 0.07 and 0.74 ± 0.04 J/m2, respectively, are in general agreement with Ranade et al.'s results (Proc. Natl. Acad. Sci. U.S.A., 2002, 99, 6476), although their numerical values are somewhat different because of impurities and unaccounted bound water in the previous work. This study supports the energy crossovers previously proposed for the TiO2 polymorphs. The energetics of water adsorption were measured using a commercial Calvet microcalorimeter coupled with a gas dosing system. This permitted the calculation of differential and integral enthalpies of water adsorption that characterize how tightly water binds to rutile and anatase surfaces and the calculation of adsorption entropies, which reflect the surface mobility of adsorbed water. The integral enthalpy of tightly bound water (relative to liquid H2O standard state) is −18 kJ/mol for anatase and −40 kJ/mol for rutile. As seen previously for Al2O3, the TiO2 polymorphs with higher surface energy bind water more tightly. The calculated entropy changes for the adsorption of water on TiO2 are more negative than the entropy changes for the condensation of gaseous water to hexagonal ice. This finding suggests highly restricted mobility of molecules adsorbed at initial stages of adsorption (low coverage) and, possibly, dissociative adsorption on both rutile and anatase surfaces. However, nanoparticles contain both tightly bound water and loosely bound water. The latter is characterized by energetics of bulk water. The stabilizing water contribution to the overall energy of the system makes the hydrated nanophase samples more stable. The recommended transformation enthalpy for bulk anatase to bulk rutile is −1.7 ± 0.9 kJ/mol.

Thermodynamic properties of soddyite from solubility and calorimetry measurements

The release of uranium from geologic nuclear waste repositories under oxidizing conditions can only be modeled if the thermodynamic properties of the secondary uranyl minerals that form in the repository setting are known. Toward this end, we synthesized soddyite ((UO 2) 2(SiO 4)(H 2O) 2), and performed solubility measurements from both undersaturation and supersaturation. The solubility measurements rigorously constrain the value of the solubility product of synthetic soddyite, and consequently its standard-state Gibbs free energy of formation. The log solubility product (lg K sp) with its error (1 σ) is (6.43 + 0.20/−0.37), and the standard-state Gibbs free energy of formation is (−3652.2 ± 4.2 (2 σ)) kJ mol −1. High-temperature drop solution calorimetry was conducted, yielding a calculated standard-state enthalpy of formation of soddyite of (−4045.4 ± 4.9 (2 σ)) kJ · mol −1. The standard-state Gibbs free energy and enthalpy of formation yield a calculated standard-state entropy of formation of soddyite of (−1318.7 ± 21.7 (2 σ)) J · mol −1 · K −1. The measurements and associated thermodynamic calculations not only describe the T = 298 K stability and solubility of soddyite, but they also can be used in predictions of repository performance through extrapolation of these properties to repository temperatures.

Thermodynamic properties of lithium mica: Lepidolite

Calorimetric measurements were made on natural sample of lepidolite having the composition (K 0.80Na 0.05Ca 0.07Rb 0.16Cs 0.03)(Li 1.34Al 1.40Fe 3+ 0.01)[Si 3.25Al 0.75O 10]F 1.80(OH) 0.20 from Na–Li-type rare-element-rich pegmatites of East Sayany, Russia. High-temperature enthalpy increments were measured with a Tian–Calvet calorimeter at 444–972 K using the drop method. The resultant C p , m o ( T) equation in the interval T = 298.15–972 K was calculated: C p , m o = 316.10 + 228.12 × 10 −3 T − 50.10 × 10 5 T −2 (J K −1 mol −1) [± 0.4%] and the value of C p , m o (298.15 K) = 327.8 J K −1 mol −1 was obtained. The standard molar enthalpy of formation from the elements was determined by high-temperature drop solution calorimetry in molten lead borate at T = 973 K. The value of Δ f H m o (298.15 K) for lepidolite was found to be −6201 ± 18 kJ mol −1. The thermodynamic properties of lepidolite of idealized composition KLi 1.5Al 1.5[Si 3AlO 10]F 2 were estimated based on the experimental data obtained.

Thermochemistry of La1-xSrxFeO3-δ Solid Solutions (0.0 ≤ x ≤ 1.0, 0.0 ≤ δ ≤ 0.5)

A series of compounds with the general formula La1-xSrxFeO3-δ have been synthesized in the complete solid solution range 0.0 ≤ x ≤ 1.0 and 0.0 ≤ δ ≤ 0.5 with a variety of heat treatments. High-temperature drop solution calorimetry in molten 2PbO·B2O3 at 702 °C was performed to determine their enthalpies of formation from oxides at room temperature. The enthalpy of oxidation involved in the reaction 2F + + 0.5O2(g) = 2F + is independent of oxygen nonstoichiometry in each La1-xSrxFeO3-δ series with a given x, and further is approximately constant at −200 ± 50 kJ/mol O2 for 0 < x ≤ 0.5 and −140 ± 30 kJ/mol O2 for 0.5 < x < 1.0. The enthalpies of formation from oxides in the LaFeO3−SrFeO2.5 solid solution can be fitted either by a quadratic equation or by two straight line segments intersecting at x = 0.5. The quadratic fit gives a positive interaction parameter, 36.1 ± 4.9 kJ/mol, suggesting a tendency toward phase separation. The two linear segment models two regions of oxygen vacancy presence: dilute (random distribution) for x ≤ 0.5 and concentrated (short-range ordering) for x > 0.5. Extrapolation to the end-member (x = 1) gives the enthalpy of formation of perovskite-type SrFeO2.5 and the enthalpy of the hypothetical brownmillerite−perovskite phase transition at room temperature is estimated as 5.5 ± 4.0 kJ/mol. This small value implies extensive short-range order in the perovskite phases with high x. The enthalpies of formation from oxides in the LaFeO3−SrFeO3 solid solution are virtually independent of Sr composition when x ≤ 0.67 and are a few kJ/mol more exothermic when x ≥ 0.7. This is interpreted by phase evolutions from low symmetries to cubic.

Energetics of La 1−xA xCrO 3−δ perovskites ( A=Ca or Sr)

A series of perovskites with the general formula La 1− xA x CrO 3− δ ( A=Ca or Sr) have been synthesized in the solid solution range 0.0< x ⩽ 0.3 and 0.0⩽ δ⩽0.5 x with a variety of heat treatments. High-temperature drop solution calorimetry in molten 2PbO·B 2O 3 at 1080 K was performed to determine their enthalpies of formation from oxides at room temperature. The enthalpy of oxidation involved in the reaction 2 Cr Cr x + V O · · + 0.5 O 2 ( g ) = 2 Cr Cr · + O O x is roughly independent of oxygen nonstoichiometry ( δ) in each series with a given dopant composition, but varies with composition ( x). The values change from −620±260 to −280±80 kJ/mol O 2 when x = 0.1 –0.3 for Ca-doped samples, and from −440±150 to −290±50 kJ/mol O 2 for Sr-doped ones. This dependence of enthalpy of oxidation on composition suggests oxygen vacancies are increasingly short-range ordered in reduced samples. The higher oxidation state of chromium is stabilized by the substitution of alkaline earth ions, but with increasing doping, the enthalpy of formation of the fully oxidized sample in both Ca and Sr-doped systems becomes more endothermic. This destabilization effect is attributed to the large endothermic enthalpy of oxygen vacancy formation (395±30 kJ/mol of V O · · ) for the reaction A A x + O O x = A La ' + 0.5 V O · · + 0.5 O 2 (A=Ca or Sr) that over-rides the exothermic enthalpies of oxidation. At a given composition, Sr-doped LaCrO 3 is more stable than its Ca-doped counterpart, which is consistent with basicity arguments.

Enthalpies of formation of Ge-zeolites: ITQ-21 and ITQ-22

A series of Ge-zeolites (ITQ-21 and ITQ-22 with varying Ge content) has been investigated by high-temperature drop solution calorimetry using lead borate solvent at 973 K. The enthalpies of formation relative to a mixture of germania and silica in the quartz forms (Δ H f) at 298 K are in the range 18.9–21.9 kJ/mol. For ITQ-22, the Δ H f values are constant, ∼14.8 ± 0.4 kJ/mol, independent of Ge-content for 0.11 < Ge/(Ge + Si) < 0.24. For ITQ-21, Δ H f becomes progressively more endothermic with increasing Ge content (which corresponds to decreasing framework density or increasing molar volume), similar to the trends seen previously for ITQ-7 and ITQ-17. The relationships between the Δ H f and Ge content for various structures are discussed in terms of concentration of double four membered rings (D4MR) and Ge location in the framework.

Enthalpy of formation of LiNiO 2, LiCoO 2 and their solid solution, LiNi 1− xCo xO 2

LiCoO 2, LiNiO 2 and their solid solution, LiNi 1− x Co x O 2, are important cathode materials for lithium ion batteries. Samples in this system were synthesized by solid state reaction of Co 3O 4, NiO and Li 2CO 3 or LiOH·H 2O. Their lattice parameters were determined by Rietveld refinement. High temperature drop solution calorimetry in molten 3Na 2O·4MoO 3 and 2PbO·B 2O 3 solvents at 974 K was performed to determine the enthalpy of formation from the constituent oxides plus oxygen and the enthalpy of mixing in the solid solution series. There are approximately linear correlations between the lattice parameters, the enthalpy of formation from oxides (Li 2O, NiO and CoO) plus O 2 and the Co content in the compounds. The solid solution of LiCoO 2 and LiNiO 2 is almost ideal, showing a small positive enthalpy of mixing. The enthalpy of formation of LiCoO 2 from oxides (Li 2O, NiO and CoO) and oxygen at 298 K is −142.5±1.7 kJ/mol (from sodium molybdate calorimetry) or −140.2±2.3 kJ/mol (from lead borate calorimetry). That of LiNiO 2 is −56.2±1.5 kJ/mol (from sodium molybdate calorimetry) or −53.4±1.7 kJ/mol (from lead borate calorimetry). The cobalt compound is thus significantly more stable than its nickel analogue. The phase assemblage LiCoO 2, Li 2O and CoO is seen at a lower oxygen pressure at constant temperature than the assemblage Co 3O 4/CoO, reflecting the stabilization of Co(III) in the ternary Li–Co–O system.

Thermodynamics of CoO–MgO solid solutions

Enthalpies of mixing in Co x Mg 1 − x O solid solutions at T=298 K have been determined using high temperature drop solution calorimetry in molten sodium molybdate (3Na 2O · 4MoO 3) solvent at T=973 K. Slightly positive enthalpies of mixing were observed, which conform to a regular solution model with interaction parameter W=(5.1 ± 0.3) kJ · mol −1, which is similar to the interaction parameter calculated from previously measured activity-composition relations. Standard molar entropies S m 0 at T=298 K calculated from subambient C p data for CoO, MgO are (52.8 ± 0.1) J · K −1 · mol −1 and (28.1 ± 0.1) J · K −1 · mol −1, respectively. Integration of the C p,m/ T of the Co 0.50Mg 0.50O mixture yields an entropy of (40.3 ± 0.1) J · K −1 · mol −1. This value does not include configurational entropy from the Co/Mg site disorder. The excess entropy of Co 0.50Mg 0.50O is zero within experimental error. Heat capacities were also measured between T=298 K and T=973 K. The enthalpies of mixing do not depend on temperature in this range.

Energetics of Nanoarchitectured TiO2−ZrO2 and TiO2−MoO3 Composite Materials

High-temperature drop solution calorimetry in sodium molybdate solvent was performed on nanoarchitectured materials using a Calvet twin microcalorimeter at 975 K. Nanocrystalline TiO2−ZrO2 samples (mesoporous structure) and nanocrystalline TiO2−MoO3 samples (core−shell structure) were investigated. With the use of the measured drop solution enthalpies, the transformation enthalpies to macroscopic stable crystalline phases have been calculated. The enthalpy of transformation from amorphous to monoclinic ZrO2 obtained from this work, −50.08 ± 4.92 kJ/mol, is in reasonable agreement with the value of −58.60 ± 3.30 kJ/mol determined by Molodetsky et al. (2000). The enthalpy of transformation from amorphous to crystalline MoO3 derived from these data is −51.25 ± 2.01 kJ/mol. The enthalpy of transformation of nanophase anatase to bulk macrocrystalline rutile TiO2 is −7.02 ± 0.96 kJ/mol. The linear variation of energetics with the composition of both series, TiO2−ZrO2 and TiO2−MoO3, suggests that these materials...

Enthalpies of formation of microporous titanosilicates ETS-4 and ETS-10

The energetics of microporous titanosilicates ETS-4 (K 1.13Na 3.92Ti 3.07Si 8.17O 25·8.64H 2O) and ETS-10 (K 0.61Na 1.09Ti 1.10Si 4.98O 13·2.89H 2O) has been investigated by high-temperature drop solution calorimetry using lead borate as the solvent at 974 K. Combining the measured heats of drop solution with the published enthalpies of drop solution and formation for the constituent oxides, the standard enthalpies of formation from the oxides ( ΔH 0 f,ox) and from the elements ( ΔH f,el 0) for both phases were derived for the first time. The obtained values (in kJ/mol) are as follows: ΔH f,ox 0(ETS-4)=−818.5±13.1, ΔH f,el 0(ETS-4)=−14,642.8±15.9, ΔH f,ox 0(ETS-10)=−262.2±3.1, and ΔH f,el 0(ETS-10)=−6995.2±6.1. Comparison between the ΔH f,ox 0 (or ΔH f,el 0) values of the two phases suggests that ETS-4 is thermodynamically more stable than ETS-10 with respect to the oxides (or the elements) at 298 K and 1 atm. This behavior can largely be attributed to the higher degree of hydration of ETS-4 than that of ETS-10.

Thermochemistry of Pure-Silica Zeolites

A series of pure-silica molecular sieves (structural codes AST, BEA, CFI, CHA, IFR, ISV, ITE, MEL, MFI, MWW, and STT) is investigated by high-temperature drop solution calorimetry using lead borate solvent at 974 K. The enthalpies of transition from quartz at 298 K (in kJ/mol) are AST, 10.9 ± 1.2; BEA, 9.3 ± 0.8; CFI, 8.8 ± 0.8; CHA, 11.4 ± 1.5; IFR, 10.0 ± 1.2; ISV, 14.4 ± 1.1; ITE, 10.1 ± 1.2; MEL, 8.2 ± 1.3; MFI, 6.8 ± 0.8; MWW, 10.4 ± 1.5; and STT, 9.2 ± 1.2. The range of energies observed is quite narrow at only 6.8−14.4 kJ/mol above that of quartz, and these data are consistent with and extend the earlier findings of Petrovic et al. The enthalpy variations are correlated with the following structural parameters: framework density, nonbonded distance between Si atoms, and framework loop configurations. A strong linear correlation between enthalpy and framework density is observed, implying that it is the overall packing quality that determines the relative enthalpies of zeolite frameworks. The presence of internal silanol groups is shown to result in a slight (≤2.4 kJ/mol) destabilization of the calcined molecular sieves by comparing calorimetric data for MFI and BEA samples synthesized in hydroxide (containing internal silanol groups) and fluoride (low internal silanol group density) media.

Effect of Framework and Layer Substitution in Manganese Dioxide Related Phases on the Energetics

The energetics of a set of MnO2-related phases having a framework or a layer structure were determined by high-temperature drop solution calorimetry at 977 K using sodium molybdate as a solvent. Enthalpies of formation were calculated from the measured enthalpies of drop solution. In these materials, different metal cations can be incorporated through framework, tunnel, and interlayer substitution. The stability of the structure depends mostly on the nature and the amount of the tunnel (or interlayer) cations. The enthalpy of formation of small-OL-1(Na0.04) is more exothermic than that of large-OL-1(Na0.26). However, framework substitution of Ni or Cu destabilizes the structure; [doped]-OL-1 or [doped]-OMS-1 materials are less stable in enthalpy than OL-1 or OMS-1. The energetics are more sensitive to the cations incorporated into the tunnels than to the cations substituting in the framework. A trend has been observed between the enthalpy of formation of the doped materials from the oxides and the ionic radius of the dopant. The average oxidation state of the manganese does not correlate directly with the energetics. These results confirm and extend previous work on manganese dioxide. The similarity of energetics of many different structures shows that the synthesis of these metastable microporous materials is not limited by energetic constraints.