Summary
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1.
The absence of reversible polymorphic transformations in the temperature region 50–1500° was established for the following oxides: Y2O3, La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Dy2O3, Ho2O3, Er2O3, Tu2O3 and Yb2;O3, as a result of high-temperature X-ray diffraction study and thermal analysis.
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2.
The presence of irreversible transitions in the oxides Nd2O3, Sm2O3, Eu2O3, Gd2O3 and their absence at temperatures of 100–1500° for the oxides Y2O3, Dy2O3, Ho2O3, Er2O3, Tb2O3, Tu2O3 was confirmed by X-ray diffraction studies.
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3.
The impossibility of producing the low-temperature C-form of lanthanum oxide by methods of decomposition of oxygen salts and the hydroxide by heating under vacuum at pressures from 760 to 1 mm Hg was demonstrated.
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4.
The C-form of neodymium oxide was produced both by decomposition of the nitrate and by decomposition of neodymium carbonate, oxalate, and hydroxide.
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5.
The reversible transitions C → A Nd2O3 and C → B Sm2O3 are accompanied by intensive gas evolution (1.5–2% by weight).
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6.
It was hypothesized that the low-temperature forms of the oxides of neodymium, samarium, gadolinium, and europium are metastable formations, possessing thermodynamic stability within their temperature interval of existence only, as a result of extraneous ions introduced into the lattice of the oxide.
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Additional information
Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimisheskaya, No. 7, pp. 1131–1138, July, 1965