1070-4272/03/7607-1031$25.00C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 7, 2003, pp. 1031!1034. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 7,
2003, pp. 1063!1066.
Original Russian Text Copyright + 2003 by Skrobot, Kuchaeva, Romanov, Grebenshchikov.
AND INDUSTRIAL INORGANIC CHEMISTRY
Subsolidus Phase Relationships in the Er
V. N. Skrobot, S. K. Kuchaeva, D. P. Romanov, and R. G. Grebenshchikov
Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, St. Petersburg, Russia
Received March 18, 2003
system was studied by the annealing and quenching method using X-ray phase,
thermal, and chemical analyses. A schematic subsolidus diagram of phase relationships was constructed.
In recent decades, there has been a great deal of
interest in multicomponent oxide systems  owing
to the fact that phases of various chemical composi-
tions and structures, existing in such systems, have
practically important properties. In particular, it was
found that complex oxides existing in the systems
Ln3M3Rh3O[43 6] (Ln is a rare-earth element and
M, an alkaline-earth element) have interesting elec-
trical, magnetic, and catalytic properties. The pur-
poseful search for new mixed oxides in these and even
more complicated similar systems should be based
on the physicochemical analysis of simpler oxide
systems M3Rh3O and Ln3Rh3O along with develop-
ment of synthetic methods. Of prime importance are
the phase diagrams in the subsolidus region.
This work continues the study of phase relation-
ships in systems containing rare-earth and rhodium
sesquioxides . Our goal was to study in detail
the subsolidus phase relationships in the Er
system in air at temperatures of up to 1600oC
and to construct the corresponding phase diagram.
The fact that the mixed oxide ErRhO
is formed in
the system Er3Rh3O was first reported in 1964 .
Later the synthesis and crystal-chemical and certain
physicochemical properties of this compound were
repeatedly studied ; however, phase relation-
ships in the Er3Rh3O system were not studied.
The initial reagents were erbium oxide Er
taining no less than 99.9% main substance and pure-
grade rhodium trichloride crystal hydrate RhCl
O. The prolonged oxidation of the latter com-
pound with atmospheric oxygen in the temperature
range 6503700oC yields the metastable polymorph
with a classic hexagonal corundum-type
structure . The high-temperature stable poly-
morphic form b-Rh
 was obtained by two fol-
lowing ways. The first method consisted in heat treat-
ment of the metastable form of a-Rh
950oC in air. The second method consisted in the oxi-
dation of finely dispersed metallic rhodium at 9503
1000oC in air or in an oxygen flow for no less than
20 h. Finely dispersed rhodium (metallic rhodium
black) was obtained by the reduction of rhodium tri-
chloride hydrochloric acid solution with metallic zinc.
The initial compositions for studying phase rela-
tionships were prepared from the mixtures of Er
in the molar ratios of 9 : 1, 4 : 1, 3 :1,
2:1, 3:2, 1:1, 3:5, 1:2, 1:3, 1:4, and 1:9.
When studying the equimolar composition, we also
used a mixture of Er
and finely dispersed rhodium.
These mixtures were triturated in a jasper mortar
with ethanol, dried in air, and then annealed in corun-
dum crucibles at temperatures from 600 to 1600oCat
100oC intervals. In certain cases, e.g., for the equi-
molar composition, the annealing and quenching were
carried out at 10320oC intervals. The duration of
annealing at temperatures of up to 1000oC reached
150 h, and above 1000oC it was up to 75 h. After
intermediate annealings for more than 20 h, samples
were homogenized by trituration. Up to 1000oC, an-
nealings were performed in a SNOL-I4 electric fur-
nace. In the experiments at higher temperatures, we
used an electric furnace with a heater made from a
platinum3rhodium, Pt/Rh (30%), wire. Annealing and
quenching were performed in air. During the iso-
thermal annealing, the temperature was held constant
with an accuracy of no less than +10oC.
The phase composition of the initial reagents and
mixtures and also of samples after annealing and
quenching was determined with DRON-3 and Siemens
D 500 HS X-ray diffractometers. We used CuK
radiation with a nickel filter. Scanning was carried