Article pubs.acs.org/JPCC
Atomistic Observation of Phase Transitions in Calcium Sulfates under Electron Irradiation Fan Cao,† He Zheng,† Shuangfeng Jia,† Xueshi Bai,‡ Lei Li,† Huaping Sheng,† Shujing Wu,† Wei Han,† Minmin Li,† Guangyu Wen,† Jin Yu,‡ and Jianbo Wang*,† †
School of Physics and Technology, Center for Electron Microscopy and MOE Key Laboratory of Artificial Micro- and Nano-structures, Wuhan University, Wuhan 430072, China ‡ Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, Villeurbanne 69622 Cedex, France S Supporting Information *
ABSTRACT: The detailed study of phase transition processes among various calcium sulfates is still insufficient in spite of its importance in artificial and natural processes. Here, the phase transformation γ-CaSO4 → β-CaSO4 → CaO is induced by electron beam irradiation and directly observed inside the transmission electron microscope (TEM). Relying on the real-time atomic-scale observation, the topological transition from γ-CaSO4 (hexagonal) to β-CaSO4 (orthorhombic) is investigated in detail, and the orientation relationship is determined: [0001]H//[001]O and (1010̅ )H//(010)O. Furthermore, three βCaSO4 variants related by 120° rotation are observed, which is theorized to occur during the transformation from hexagonal to orthorhombic structure. The possible transition mechanism is thus discussed. This work offers detailed information on the transition mechanism concerning the calcium sulfates, which might facilitate their industrial applications and possibly further understanding of rock deformation in the earth crust.
■
INTRODUCTION As one of the most abundant minerals on Earth, calcium sulfates play important roles in artificial and natural processes,1,2 manifested by their extensive applications in industrial (building materials1,3 with the ability of fire protection4),5 medical,6,7 agricultural (scaling agricultural drainage water8 or used as fertilizer9), and even cultural (used for ground painting by ancient Southern European painters10) domains. Generally, there are three sorts of calcium sulfates distinguished by the degree of dehydration: gypsum (CaSO4·2H2O), hemihydrate (CaSO4·0.5H2O), and anhydrite (β-CaSO4 and γ-CaSO4),11 and the dehydration process, probably associated with the structural rearrangement, could occur with the increasing temperature. Since the different crystal phases would exhibit distinct physical and chemical properties compared to each other, understanding the dehydration-induced phase nucleation/transition is of wide technological relevance especially for exploring the geological processes in the earth’s crust, e.g., the rock deformation and even the generation of earthquakes.12−15 In this context, considerable efforts have been dedicated to characterize the different phases formed during the dehydration process by employing various experimental techniques, such as infrared spectroscopy,16 Raman spectroscopy,12 and neutron and X-ray diffraction,17−19 based upon which a possible dehydration pathway, CaSO4·2H2O → CaSO4·0.5H2O → γCaSO4 → β-CaSO4, has been proposed previously.12,19−21 Nonetheless, because most of these studies have mainly focused on the structural investigation of single phases, the detailed © XXXX American Chemical Society
structural relationships among them as well as the relative phase transition mechanisms remain obscure. According to neutron and X-ray diffraction results, the phase transitions were speculated to be topological with preserved Ca2+ and SO42− chains,17,22 which has not been confirmed yet. Compared with the above-mentioned techniques, i.e., infrared/ Raman spectroscopy and neutron/X-ray diffraction, transmission electron microscopy/microscope (TEM) shows its advantages in providing the direct atomic-scale phase transition details and thus the structural relationship among different phases.23 Herein, applying the electron beam (e-beam) irradiation inside TEM as an external stimulus,24−27 we report the atomistic observation of the structural transition of calcium sulfates, with the sequence γ-CaSO4 → β-CaSO4 → CaO. Furthermore, the possible transition mechanisms are discussed.
■
EXPERIMENTAL SECTION Preparation of Calcium Sulfate Nanocrystals (NCs). The calcium sulfate NCs were prepared by a simple method. First, aluminum plasma was induced on the surface of a pure aluminum (99.99%) by the laser beam, and then a glass sheet was positioned beside the aluminum plasma. In subsequence, the glass was ablated by the high-temperature and -pressure aluminum plasma, and thus some white powders were generated on the surface of the glass sheet. Details of the plasma-induced setup are described elsewhere.28 Finally, the Received: August 3, 2015 Revised: September 2, 2015
A
DOI: 10.1021/acs.jpcc.5b07508 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
interestingly, under e-beam irradiation, the single crystalline γCaSO4 were pretty unstable and would transform into polycrystalline CaO (JCPDS 82-1691) after several minutes (Figure 1e), which is confirmed by the lower intensities of S and O peaks after the phase transition as illustrated in the corresponding EDS spectra recorded from the NC before (dashed lines) and after the transition (solid lines) (Figure 1f). The C and Cu signals originate from the carbon-coated copper grid, and the Si signal results from the NCs which are unintentionally introduced within the sample preparation process. It has to be pointed out that γ-CaSO4 has similar crystal structure with those of CaSO4·0.5H2O (lattice parameters: aPT = 6.948 Å, bPT = 6.929 Å, and cPT = 6.335 Å; α = 90°, β = 90.23°, and γ = 120°, the subscript “PT” denotes the pseudotrigonal structure of CaSO4·0.5H2O),29 which makes it difficult to distinguish CaSO4·0.5H2O and γ-CaSO4 based on SAED patterns. However, the energy required for water loss (32.9 kJ mol−1)30 is much less than the decomposition energy (512.4 kJ mol−1)31 of CaSO4. On the other hand, H and O atoms are much more sensitive to electron irradiation compared with S and Ca elements (discussed in the later section). As such, the water molecules in CaSO4·0.5H2O can be removed easily by heating or drying.11 As a result, inside the TEM (with electron irradiation and high vacuum/very low humidity), it is more reasonable to index the SAED patterns based on the γ-CaSO4 structure.19 In addition, the atomic-scale phase transition process, γCaSO4 → CaO, has been revealed by the in situ HRTEM technique. An intermediate product, i.e., β-CaSO4 (with lattice parameters of aO = 6.993 Å, bO = 6.995 Å, and cO = 6.245 Å, and “O” represents the orthorhombic structure) (JCPDS 862270), was found during the transition. Specifically, the hexagonal γ-CaSO4 (Figure 2a) would first transform into orthorhombic β-CaSO4 (Figure 2b), and after 120 s only a small region of β-CaSO4 was visible (Figure 2c, confirmed by
white powders were scratched off the glass sheet, sonicated in ethanol for about 2 min, and then dropped onto an ultrathin carbon-coated copper grid for TEM experiments. Characterization. The bright-field (BF) images and selected area electron diffraction (SAED) patterns were taken with a JEOL JEM-2010 (HT) electron microscope equipped with a LaB6 electron source, while high-resolution TEM (HRTEM) images and the energy-dispersive X-ray spectroscopy (EDS) spectra were obtained inside a JEOL JEM-2010 FEF (UHR) electron microscope equipped with a field emission gun and an Omega-type in-column energy filter system.
■
RESULTS AND DISCUSSION There are two types of as-synthesized nanocrystals (NCs), one with smaller size (less than 100 nm in diameter) and one with lager size (nearly 1 μm in diameter), as shown in Figure 1a and
Figure 1. (a, c) BF images of pristine calcium sulfate NCs. (b, d) Corresponding SAED patterns of the circled areas in (a) and (c), respectively. (e) SAED pattern with further e-beam irradiation of the NC in (c). (f) EDS spectra recorded from the NC before and after phase transformation. The peak intensity of Ca is set to be constant.
1c, respectively. Figure 1a shows the BF image of the smaller NCs which are identified to be γ-CaSO4 (with lattice parameters of aH = 6.990 Å and cH = 6.340 Å, and “H” represents the hexagonal structure) (JCPDS 73-1942) based on the corresponding ring-like polycrystalline diffraction pattern (Figure 1b). In contrast, the NC with larger size (Figure 1c) is found to be single crystalline γ-CaSO4, and the corresponding SAED pattern can be indexed as the [0001] zone axis. More
Figure 2. (a−d) Time-lapsed images showing the structural evolution from γ-CaSO4 to CaO induced by the e-beam irradiation. Insets are the corresponding fast Fourier transformation (FFT) patterns, except that in (b) the FFT pattern corresponds to the white-boxed area. B
DOI: 10.1021/acs.jpcc.5b07508 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C the FFT pattern, with only two spots left), in accordance with the collapse of Ca2+ and SO42− chains. Finally, after 300 s ebeam illumination, nanocrystalline CaO NCs were generated (Figure 2d), which might be explained by the recrystallization of CaO.32 Despite that the transformation from γ-CaSO4 to β-CaSO4 has been reported,11,18 the detailed orientation relationship (OR) between them was rarely observed. In the current experiment, the OR is identified as [0001]H//[001]O, (101̅0)H//(010)O (Figure 2b). Such an OR can be intuitively understood by comparing the crystal structures of γ-CaSO4 and β-CaSO4 (Figure 3a), according to which the atomic
Figure 4. (a−d) Detailed atomistic images revealing the phase transition from γ-CaSO4 to β-CaSO4. The inset in (a) is the corresponding FFT pattern.
single β-CaSO4 variant mentioned above (red diffraction spots in Figure 5b). Instead, such a pattern can be explained by the coexistence of three β-CaSO4 variants related by 120° rotation as illustrated in Figure 5d. Since the lengths of the a and b axes in the β-CaSO4 lattice cell are approximately equal (aO = 6.993 Å, bO = 6.995 Å, cO = 6.245 Å), the ORs between original hexagonal γ-CaSO4 and the three orthorhombic β-CaSO4 variants could be approximately expressed as follows ⎡1/2 ⎡a⎤ ⎢b ⎥ = ⎢ ⎢ −1 ⎢ ⎥ ⎣ c ⎦H ⎢⎣ 0 Figure 3. (a) Structural models of γ-CaSO4 and β-CaSO4 viewed along the [0001]H and [001]O directions, respectively. (b, c) Atomic arrangements of (1010̅ )H and (010)O planes.
arrangements within the (1010̅ )H plane (Figure 3b) are similar to those located in the (010)O plane (Figure 3c) but quite distinct with those located in the (100)O plane (Figure S1 in Supporting Information (SI)). Hence, the transformation process probably occurred via the local atomic rearrangement with conservation of the structural units of the (101̅0)H plane, and a similar nucleation way was reported in the phase transition of WO3.23 A more detailed γ-CaSO4 to β-CaSO4 phase transition process is presented in Figure 4, whereas the region of β-CaSO4 grows (indicated with dashed white box in Figure 4b, 4c, and 4d) (see also Movie 1 in SI) along the [010]O direction, validating the above proposed transition mechanism, i.e., based on the atomic rearrangement of the (101̅0)H//(010)O planes. Meanwhile, three β-CaSO4 variants related by 120° rotation were consistently found during such a phase transition. Figure 5a and 5b present the experimental and simulated SAED patterns with the coexistence of the γ-CaSO4, β-CaSO4, and CaO crystals, respectively. It is noted that, besides the singlecrystalline γ-CaSO4 (Figure 5c) and polycrystalline CaO phases (Figure 5b), the pattern could not be indexed based on the
3 /2 0 ⎤⎡ a ⎤ ⎥⎢ ⎥ 0 0 ⎥⎢ b ⎥ 0 1 ⎥⎦⎣ c ⎦OI
(1)
⎡1/2 − 3 /2 0 ⎤ a ⎡a⎤ ⎢ ⎥⎡ ⎤ ⎢b ⎥ = ⎢ ⎢ ⎥ 1/2 3 /2 0 ⎥⎢b ⎥ ⎢ ⎥ ⎥⎣ c ⎦ ⎣ c ⎦H ⎢ ⎣ 0 0 1 ⎦ OII
(2)
⎡ −1 0 0 ⎤⎡ a ⎤ ⎡a⎤ ⎢ ⎢b ⎥ = 1/2 − 3 /2 0 ⎥⎢b ⎥ ⎢ ⎥⎢ ⎥ ⎢ ⎥ ⎣ c ⎦H ⎣⎢ 0 0 1 ⎥⎦⎣ c ⎦OIII
(3)
whereas the subscripts OI, OII, and OIII represent the three orthorhombic β-CaSO4 variants, correspondingly. Relying on the structural model and the above ORs (Figure 5d), the simulated composited diffraction pattern (Figure 5b) from the original hexagonal structure γ-CaSO4 (Figure 5c), three orthorhombic variants (Figure 5e−g), and the three polycrystalline CaO diffraction rings (yellow rings in Figure 5b) matches well with the experimental SAED pattern (Figure 5a). Such variants can be as well visualized in Figure 2b, where the other two variants were indicated by the arrowheads. The appearance of three variants related by 120° rotation can be well-understood by the group theory, which predicts that the phase transition from the hexagonal phase with higher symmetry to the orthorhombic phase with lower symmetry is accompanied by the loss of 6-fold symmetry along the [0001]H C
DOI: 10.1021/acs.jpcc.5b07508 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 5. (a,b) Experimental and simulated diffraction patterns based on the coexistence of γ-CaSO4, three β-CaSO4 variants, and polycrystalline CaO. (c) The simulated diffraction pattern of γ-CaSO4 along the [0001]H direction. (d) Schematic illustration of the OR between γ-CaSO4 and the three variants. (e−g) The simulated diffraction patterns of the three orthorhombic variants related by 120° rotation (red, green, and blue for variants OI, OII, and OIII, respectively).
predicted by the group theory. The e-beam irradiation induced elastic collision effect was supposed to activate the transformations without significantly increasing the temperature.
and the generation of variants linked by the lost 6-fold symmetry.33−36 Finally, the NCs would again transform into pure polycrystalline CaO with further e-beam irradiation (Figure S2 in SI). It should be noted that such transition processes were welldocumented to occur with the increasing temperature, i.e., about 600 K for γ-CaSO4 → β-CaSO4 and at least 1200 K for the decomposition of CaSO 4 into CaO, SO 2 , and O2.12,18,19,31,37 However, the maximum temperature rise induced by e-beam irradiation in the current experiment was estimated to be approximately 0.5 and 25.4 K when obtaining the SAED patterns and HRTEM images, respectively (see details of calculation in SI), which is certainly not sufficient to explain the phase transition. Therefore, the heating effect was not the crucial factor to activate the transformations, and the elastic two-body collision effect of electrons and atoms is believed to activate the transitions.27 The maximum acquired kinetic energy (Emax) of an atom in the collision can be expressed by eq 427 Emax
2E1(2m0c 2 + E1) P2 = = 2M Mc 2
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.5b07508. Atomistic observation of the γ-CaSO4 → β-CaSO4 phase transition. Figure S1, atomic arrangements of the (101̅0)H, (010)O, and (100)O planes. Figure S2, the SAED patterns obtained during the transition. Calculation of the temperature rising induced by electron irradiation (PDF) Movie 1 (AVI)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +86-27-6875-2481, ext. 8132. Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. F. Cao and H. Zheng contributed equally.
(4)
where E1 and m0 represent the kinetic energy of the incident electron and the rest mass of an electron, respectively; M is the mass of the atom; and c is the velocity of light. In the current experiment, the acceleration voltage is 200 kV, and the calculated Emax is 520.6 eV for H, 32.5 eV for O, 16.3 eV for S, and 13.0 eV for Ca. Considering the relatively lower decomposition energy for calcium sulfates (512.4 kJ mol−1, namely, 5.3 eV per molecule), it is reasonable to expect that the energetic incident electrons can cause the phase transition γCaSO4 → β-CaSO4 → CaO.
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the 973 Program (No. 2011CB933300), the National Natural Science Foundation of China (Nos. 51271134, J1210061), the Fundamental Research Funds for the Central Universities, the CERS-1-26 (CERSChina Equipment and Education Resources System), and the China Postdoctoral Science Foundation (No. 2013M540602, 2014T70734).
■
CONCLUSIONS In summary, the phase transition pathway γ-CaSO4 → β-CaSO4 → CaO was directly observed by manipulating the e-beam inside TEM. According to the atomic-scale observation, the OR between γ-CaSO4 and β-CaSO4 was determined to be [0001]H//[001]O and (101̅0)H//(010)O. Additionally, three β-CaSO4 variants related by 120° rotation were verified during the transition from γ-CaSO4 to β-CaSO4, which is well-
■
REFERENCES
(1) Charola, A. E.; Pühringer, J.; Steiger, M. Gypsum: a Review of Its Role in the Deterioration of Building Materials. Environ. Geol. 2007, 52, 339−352. (2) Van Driessche, A.; Benning, L.; Rodriguez-Blanco, J.; Ossorio, M.; Bots, P.; García-Ruiz, J. The Role and Implications of Bassanite as
D
DOI: 10.1021/acs.jpcc.5b07508 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C a Stable Precursor Phase to Gypsum Precipitation. Science 2012, 336, 69−72. (3) Kumar, S. Fly Ash−lime−phosphogypsum Hollow Blocks for Walls and Partitions. Build. Environ. 2003, 38, 291−295. (4) Weber, B. Heat Transfer Mechanisms and Models for a Gypsum Board Exposed to Fire. Int. J. Heat Mass Transfer 2012, 55, 1661− 1678. (5) Aagli, A.; Tamer, N.; Atbir, A.; Boukbir, L.; El Hadek, M. Conversion of Phosphogypsum to Potassium Sulfate. J. Therm. Anal. Calorim. 2005, 82, 395−399. (6) Hesaraki, S.; Moztarzadeh, F.; Nemati, R.; Nezafati, N. Preparation and Characterization of Calcium Sulfate−biomimetic Apatite Nanocomposites for Controlled Release of Antibiotics. J. Biomed. Mater. Res., Part B 2009, 91B, 651−661. (7) Cooper, J. J.; Brayford, M. J.; Laycock, P. A. A New Acoustic Method to Determine the Setting Time of Calcium Sulfate Bone Cement Mixed with Antibiotics. Biomed. Mater. 2014, 9, 045006. (8) Le Gouellec, Y. A.; Elimelech, M. Calcium Sulfate (Gypsum) Scaling in Nanofiltration of Agricultural Drainage Water. J. Membr. Sci. 2002, 205, 279−291. (9) Lobb, W.; Rothbaum, H. The Use of Anhydrite as a Fertiliser. N. Z. J. Agric. Res. 1969, 12, 119−124. (10) Genestar, C. Characterization of Grounds Used in Canvas and Sculpture. Mater. Lett. 2002, 54, 382−388. (11) Freyer, D.; Voigt, W. Crystallization and Phase Stability of CaSO4 and CaSO4 − based Salts. Monatsh. Chem. 2003, 134, 693− 719. (12) Comodi, P.; Kurnosov, A.; Nazzareni, S.; Dubrovinsky, L. The Dehydration Process of Gypsum under High Pressure. Phys. Chem. Miner. 2012, 39, 65−71. (13) Griggs, D.; Handin, J. Observations on Fracture and a Hypothesis of Earthquakes. Mem. - Geol. Soc. Am. 1960, 79, 347−364. (14) Heard, H. C.; Rubey, W. W. Tectonic Implications of Gypsum Dehydration. Geol. Soc. Am. Bull. 1966, 77, 741−760. (15) White, S.; Knipe, R. Transformation- and Reaction-enhanced Ductility in Rocks. J. Geol. Soc. 1978, 135, 513−516. (16) Putnis, A.; Winkler, B.; Fernandez-Diaz, L. In situ IR Spectroscopic and Thermogravimetric Study of the Dehydration of Gypsum. Mineral. Mag. 1990, 54, 123−128. (17) Abriel, W.; Reisdorf, K.; Pannetier, J. Dehydration Reactions of Gypsum: A Neutron and X-ray Diffraction Study. J. Solid State Chem. 1990, 85, 23−30. (18) Ballirano, P.; Melis, E. The Thermal Behaviour of γ-CaSO4. Phys. Chem. Miner. 2009, 36, 319−327. (19) Seufert, S.; Hesse, C.; Goetz-Neunhoeffer, F.; Neubauer, J. Quantitative Determination of Anhydrite III from Dehydrated Gypsum by XRD. Cem. Concr. Res. 2009, 39, 936−941. (20) Yamamoto, H.; Kennedy, G. Stability Relations in the System CaSO4-H2O at High Temperatures and Pressures. Am. J. Sci. A 1969, 267, 550−557. (21) Ballirano, P.; Melis, E. Thermal Behaviour and Kinetics of Dehydration of Gypsum in Air from in situ Real-time Laboratory Parallel-beam X-ray Powder Diffraction. Phys. Chem. Miner. 2009, 36, 391−402. (22) Dent-Glasser, L. Topotactic Reactions in Inorganic Oxycompounds. Q. Rev., Chem. Soc. 1962, 16, 343−360. (23) Figlarz, M.; Gérand, B.; Delahaye-Vidal, A.; Dumont, B.; Harb, F.; Coucou, A.; Fievet, F. Topotaxy, Nucleation and Growth. Solid State Ionics 1990, 43, 143−170. (24) Zhang, K.; Wang, J.; Lu, X.; Li, L.; Tang, Y.; Jia, Z. Structural Evolution of Hydrothermal-synthesized Ni(SO4)0.3(OH)1.4 Nanobelts During ex situ Heat Treatment and in situ Electron Irradiation. J. Phys. Chem. C 2008, 113, 142−147. (25) Xu, T.; Sun, L. Dynamic In-situ Experimentation on Nanomaterials at the Atomic Scale. Small 2015, 11, 3247−3262. (26) Zheng, H.; Liu, Y.; Cao, F.; Wu, S.; Jia, S.; Cao, A.; Zhao, D.; Wang, J. Electron Beam-assisted Healing of Nanopores in Magnesium Alloys. Sci. Rep. 2013, 3, 1920.
(27) Sun, X.; Wang, B.; Kempson, I.; Liu, C.; Hou, Y.; Gao, M. Restructuring and Remodeling of NaREF4 Nanocrystals by Electron Irradiation. Small 2014, 10, 4711−4717. (28) Bai, X.; Ma, Q.; Motto-Ros, V.; Yu, J.; Sabourdy, D.; Nguyen, L.; Jalocha, A. Convoluted Effect of Laser Fluence and Pulse Duration on the Property of a Nanosecond Laser-induced Plasma into an Argon Ambient Gas at the Atmospheric Pressure. J. Appl. Phys. 2013, 113, 013304. (29) Ballirano, P.; Maras, A.; Meloni, S.; Caminiti, R. The Monoclinic I2 Structure of Bassanite, Calcium Sulphate Hemihydrate (CaSO4· 0.5H2O). Eur. J. Mineral. 2001, 13, 985−993. (30) Sarma, L.; Prasad, P.; Ravikumar, N. Raman Spectroscopic Study of Phase Transitions in Natural Gypsum. J. Raman Spectrosc. 1998, 29, 851−856. (31) Lau, K. H.; Cubicciotti, D.; Hildenbrand, D. L. Effusion Studies of the Thermal Decomposition of Magnesium and Calcium Sulfates. J. Chem. Phys. 1977, 66, 4532−4539. (32) Jenc̆ic̆, I.; Bench, M. W.; Robertson, I. M.; Kirk, M. A. Electronbeam-induced Crystallization of Isolated Amorphous Regions in Si, Ge, GaP, and GaAs. J. Appl. Phys. 1995, 78, 974−982. (33) Wang, R.; Gui, J.; Zhu, Y.; Moodenbaugh, A. R. Crystallographic Analysis of Orientational Domain Variants and Charge-ordered Domains in La0.33Ca0.67MnO3. Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 63, 144106. (34) Jia, S.; Sang, H.; Zhang, W.; Zhang, H.; Zheng, H.; Liao, L.; Wang, J. Ordered and Twinned Structure in Hexagonal-based Potassium Tungsten Bronze Nanosheets. J. Appl. Crystallogr. 2013, 46, 1817−1822. (35) Wen, Y. H.; Wang, Y.; Chen, L. Q. Phase-field Simulation of Domain Structure Evolution during a Coherent Hexagonal-toorthorhombic Transformation. Philos. Mag. A 2000, 80, 1967−1982. (36) Zheng, H.; Wang, J.; Xu, Z.; Gui, J. Intra-layer Ordering and Inter-layer Disordering of the Li2MnO3 Phase in Li1.07Mn1.93O4−δ Cathode Materials: Electron Diffraction Investigation and DIFFaX simulation of X-ray Diffraction Patterns. J. Appl. Crystallogr. 2014, 47, 879−886. (37) Badens, E.; Llewellyn, P.; Fulconis, J. M.; Jourdan, C.; Veesler, S.; Boistelle, R.; Rouquerol, F. Study of Gypsum Dehydration by Controlled Transformation Rate Thermal Analysis (CRTA). J. Solid State Chem. 1998, 139, 37−44.
E
DOI: 10.1021/acs.jpcc.5b07508 J. Phys. Chem. C XXXX, XXX, XXX−XXX
