Thermodynamics and structural chemistry of compounds in the system MgOTiO2

Wechsler, B. A.; Navrotsky, Alexandra

doi:10.1016/0022-4596(84)90262-7

Cited by 126 publications

(101 citation statements)

References 28 publications

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“…In Fig. 4(b), data reported by Wechsler and Navrotsky 10) are also plotted. The occupation of Al 2 TiO 5 and Fe 2 TiO 5 did not depend on the annealing temperature, while that of MgTi 2 O 5 depended on the annealing temperature.…”

Section: Cation Distributionmentioning

confidence: 99%

“…The change in the distribution of the two types of cations in the two octahedral sites is very interesting. Wechsler and Navrotsky studied the dependence of the cation distribution in MgTi 2 O 5 on temperature according to the change in the dimension of the c-axis 10) and found that occupancy by Ti 4+ in the 4c site decreased with decreasing temperature. Brown and Navrotsky 11) 14) studied the cation distribution of Al 2 TiO 5 by high temperature neutron and X-ray diffractometry and reported an almost random distribution and little preference of Ti 4+ ion for the 4c site below 800°C, which was the same tendency found by Norberg.…”

Section: Introductionmentioning

confidence: 99%

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Cation distribution of pseudobrookite-type titanates and their phase stability

Ohya

Kawauchi

Ban

2017

J. Ceram. Soc. Japan

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Pseudobrookite-type titanate has two types of oxide octahedra for different cation types. The cation distributions in the octahedra of three pseudobrookite type oxides, Al 2 TiO 5 , MgTi 2 O 5 and Fe 2 TiO 5 , and in a solid solution of 0.5Al 2 TiO 5 0.5MgTi 2 O 5 were studied by the Rietveld method. The analysis revealed that the cation distributions of Al 2 TiO 5 and Fe 2 TiO 5 did not depend on the annealing temperature, whereas that of MgTi 2 O 5 depended on the annealing temperature. The estimated cation distributions determined by the Rietveld method agreed with those determined by bond valence sum estimation. The configuration entropies of Al 2 TiO 5 and Fe 2 TiO 5 were almost the same as that of the maximum value of the random distribution of cations. Although the configuration entropy stabilized Al 2 TiO 5 thermodynamically, the decomposition of Al 2 TiO 5 should be attributed to the stable nature of corundum, and the rather "stretched" structure of Al 2 TiO 5 would also cause its instability at low temperature.

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Section: Cation Distributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cation distribution of pseudobrookite-type titanates and their phase stability

Ohya

Kawauchi

Ban

2017

J. Ceram. Soc. Japan

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“…An understanding of the structural variations observed in these compounds and their effects on the stability relations in the system MgO-TiO2 would be beneficial for estimating properties in more complex systems with related structures. The thermodynamics of these materials has recently been investigated by Wechsler & Navrotsky (1984). In order to characterize the structural state of samples used for thermochemical measurements, we have refined the structures of these compounds.…”

Section: Introductionmentioning

confidence: 99%

Structure refinements of Mg₂TiO₄, MgTiO₃ and MgTi₂O₅ by time-of-flight neutron powder diffraction

Wechsler¹,

Dreele²

1989

Acta Crystallogr B Struct Sci

164

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Rietveld refinements using time-of-flight neutron diffraction data are reported for two forms of Mg2TiO4 (Mr=160-51), MgTiO3 (Mr=120.20) and two samples of MgTi205 (Mr = 200" 10). The compounds were synthesized at 1673K and subsequently annealed and quenched from other temperatures. All data were collected at room temperature on a 10 m powder diffractometer at a nominal scattering angle of 150 ° 20. Mg2TiO4 annealed at 973 K has the spinel structure, space group Fd3m, with a= 8.4376(5),~, V=600.71(ll)A 3, Z=8. Mg2TiO4 prepared at 773 K is tetragonal, space group P4122, a = 5.9748 (5), c = 8.414 (7) A, V= 300.37 (7) A 3, Z = 4. Final weighted-profile R values are 0.0376 and 0-0327 for the cubic and tetragonal spinels, respectively. In the cubic form, Mg and Ti are disordered in a single octahedral site to form a nearly perfect inverse spinel, although there may be considerable short-range order. The tetragonal structure is a slight distortion of the cubic one, with two inequivalent octahedral sites over which the Mg and Ti are highly, but completely, ordered. MgTiO3 annealed_at 1073 K has the ilmenite structure, space group R3, a = 5.05478 (26), c = 13.8992 (7)/~, V = 307.56 (4) A 3, Z = 6. The final Rwp is 0.0257. Mg and Ti are completely ordered between two octahedral sites, and probably remain so at temperatures up to Mg-Ti distribution in both samples is disordered, with the 1773 K sample substantially more disordered. The lattice parameters of MgTi205 are sensitive to the degree of disorder. These results have been combined with thermochemical data obtained on the same specimens to derive an understanding of the effects of order-disorder on the phase-stability relations of these compounds.

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“…It shows higher negative deviations from ideality than that of the analogous system Mg2T i0 4-MgAl20 4 [15]. At moderate temperatures it is known that pure Mg2T i0 4 exhibits a large degree of shortrange order in the octahedral sublattice [16]. Replac ing Mg2 + by the transition metal cation Co2 + we may assume that similar short-range ordering appears on a larger scale, which decreases the lattice constant.…”

Section: Resultsmentioning

confidence: 99%

Some Aspects of Spinodal Decomposition in Spinel Solid Solutions

Burkert

Grüne

Schmalzried

et al. 1995

Zeitschrift Für Naturforschung A

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Dedicated to Professor Dr. E. Wicke on occasion of his 80th birthday Decomposition morphologies of supersaturated spinel solid solutions in the quasi-binary system Co2Ti04-CoAl20 4 at 973 K show all pertinent features of spinodal decomposition. Since the de composition morphology may not be considered as sufficient evidence for a spinodal process, the thermodynamics of the spinel solid solutions and the linear transport theory of spinodal decompo sition were combined to corroborate the experimental results of the early decomposition reaction.Simultaneous ordering, a common property of ternary and higher nonequilibrium solid solutions, was also observed. These ordering processes occur locally in distinct regions of the spinel crystal. Moreover, the spinodal wavelength X increases in time according to X cc t, which is unusual and will be discussed in the light of cation diffusion in semiconducting oxides with two cation sublattices.

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Thermodynamics and structural chemistry of compounds in the system MgOTiO2

Cited by 126 publications

References 28 publications

Cation distribution of pseudobrookite-type titanates and their phase stability

Cation distribution of pseudobrookite-type titanates and their phase stability

Structure refinements of Mg₂TiO₄, MgTiO₃ and MgTi₂O₅ by time-of-flight neutron powder diffraction

Some Aspects of Spinodal Decomposition in Spinel Solid Solutions

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Thermodynamics and structural chemistry of compounds in the system MgOTiO2

Cited by 126 publications

References 28 publications

Cation distribution of pseudobrookite-type titanates and their phase stability

Cation distribution of pseudobrookite-type titanates and their phase stability

Structure refinements of Mg2TiO4, MgTiO3 and MgTi2O5 by time-of-flight neutron powder diffraction

Some Aspects of Spinodal Decomposition in Spinel Solid Solutions

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Structure refinements of Mg₂TiO₄, MgTiO₃ and MgTi₂O₅ by time-of-flight neutron powder diffraction