This work constitutes a closer investigation of part of the system, PbO/TeO2, with particular attention to the existence and nature of a 1∶1 molar ratio compound, following inconsistencies in previous publications. Observations on previous attempts to pull crystals from the melt are reconsidered in the light of the current work.

The central region of the PbO/TeO2 phase diagram

The dissociation of NiTe 2 O 5 and Ni 2 Te 3 O 8 was investigated between 900 and 1000 K using the mass spectrometric Knudsen effusion method. It was found that both substances evaporate incongruently according to the following reactions. 2 NiTe 2 O 5 ( s )  Ni 2 Te 3 O 8 ( s ) + TeO 2 ( g ) Ni 2 Te 3 O 8 ( s )  2 NiO ( s ) + 3 TeO 2 ( g ) From the measured equilibrium vapour pressure of TeO 2 for both reactions in the given temperature interval and from the values of C p for TeO 2 (s) and TeO 2 (g), the entropy S 298 K and C p for Ni 2 Te 3 O 8 and NiTe 2 O 5 were estimated, allowing the calculation of some thermodynamical data according to the second and third law methods. The second law heats of reactions at 298 K were found to be 283.3 ± 12.6 and 880.7 ± 25.1 kJ mol −1 and for the third law heats of reaction 269.9 ± 4.1 and 851.0 ± 8.1 kJ mol −1 for the first and second reaction respectively. The standard enthalpies of formation of Ni 2 Te 3 O 8 and NiTe 2 O 5 were found as 1549.8 ± 25.0 and 948.0 ± 37.1 kJ mol −1 respectively.

Mass spectrometric investigations of NiTe2O5 and Ni2Te3O8 at high temperatures

Vaporization studies over (NiO + Ni2Te3O8) in the Ni–Te–O system by transpiration thermogravimetry and Knudsen effusion mass spectrometry

Possible tellurites of antimony obtained by the precipitation reactions

Influence of chemical composition of nickel tellurides Nil+p Te2(O p 1.5) on oxidation during heating up to 900°C in air was investigated by thermal,X-ray and electron diffraction analysis.

B. Volavšek

Papers

Thermal investigation of NiTeO3 and the synthesis of Ni2Te3O8