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ABSTRACTS OF RECENT PUBLICATIONS
The Binary System Re-Al
by Julius C. Schuster1, Loic Perring3, Klaus W. Richter2, Herbert Ipser2, Yuri Grin4, and
Franz Weitzer1
(1 Institut für Physikalische Chemie and 2 Institut für Anorganische Chemie der Universität
Wien, Austria; 3 Institut de Chimie Minérale et Analytique, Université de Lausanne,
Switzerland; and 4 Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden,
Germany)
Journal of Alloys and Compounds 320 (2001), 224
The binary system rhenium-aluminium is characterized by the occurrence of seven
intermediate phases and two eutectics. The intermediate phases are: Re2Al, ReAl, Re4Al11,
ReAl4(h), Re8Al33-x, ReAl6, and ReAl12. They form at 14944°C (peritectoid), 106010°C
(peritectoid), 1665°C (congruent melting), 14044°C (incongruent melting), 10084°C
(polymorphic transformation), 8034°C (incongruent melting), and 7504°C (incongruent
melting), respectively. Crystal structure data and lattice parameters for all these phases are
given. The two eutectics occur (1) at 16553°C and ~74 at% Al, and (2) at 658°C and >99
at% Al.
The Ternary Ga-Ni-Sb System: Invariant Reactions
and Liquidus Surface
by Kornelia Micke, Klaus W. Richter, and Herbert Ipser
(Institut für Anorganische Chemie der Universität Wien)
Zeitschrift für Metallkunde 92 (2001), 14
The phase relationships for Ga-Ni-Sb alloys were determined by means of differential thermal
analyses along ten selected isopleths through the ternary system. From these the sequence of
invariant reactions involving the liquid phase was derived in terms of a Scheil diagram.
Furthermore, a projection of the liquidus surface was constructed for the entire composition
range. It contains a total of nine invariant four-phase reactions, seven of the transition type
and two of the eutectic type. Together with the isothermal sections at 900, 600, and 500°C
that were presented earlier this results in a full description of the phase equilibria in the
ternary Ga-Ni-Sb system as a function of composition and temperature.
Determination of the elementary jump of Co in
CoGa by quasielastic neutron scattering
by M. Kaisermayr1, J. Combet2, H. Ipser3, H. Schicketanz3, B. Sepiol1, and G. Vogl1,4
(1 Institut für Materialphysik and 3 Institut für Anorganische Chemie der Universität Wien,
Austria; 2 Institut Laue-Langevin, Grenoble, France; and 4 Hahn-Meitner Institut, Berlin,
Germany)
Phys. Rev. B 63 (2001), 054303-1
Quasielastic neutron scattering at the backscattering spectrometer IN16 at the ILL has been
used to determine the elementary jump vector of diffusing Co atoms in the B2 phase of CoGa.
Measurements have been performed on single crystals with 54 at.% Co and 64 at.% Co. For
both compositions a maximum of the quasielastic broadening has been observed near a
reciprocal lattice point corresponding to a B2 superlattice reflection. This gives unambiguous
evidence of Co diffusion via nearest neighbor jumps. From the residence times on the
antistructure sites high defect concentrations are deduced. The correlation of Co diffusion has
been found to be surprisingly weak. A diffusion mechanism is suggested which takes
advantage of the high degree of disorder and, therefore, cannot be described in terms of
defined cycles.
The Ternary Compounds In5.25Pd13Sb3.75 and In1.26PdSb0.74:
Crystal Structure and Electronic Structure Calculations
Hans Flandorfer1,*, Klaus W. Richter1, Gerald Giester2 and H. Ipser1
(1Institut für Anorganische Chemie, Währingerstrasse 42, Universität Wien, A-1090 Wien,
Austria; 2Institut für Mineralogie und Kristallographie, Althanstrasse 14, Universität Wien, A1090 Wien, Austria)
J. Solid State Chem. 164 (2001), 110
The new ternary compound In5.25Pd13Sb3.75 was found. It's crystal structure was determined
using a CCD-diffractometer at room temperature. Evaluations and refinements finally yielded
a C-centered monoclinic structure (space group: C 2/c; Pearson symbol: mC88, Z = 4) with a
= 15.189(2) Å, b = 8.799(1) Å, c = 13.602(2) Å and  = 123.83(1)°. For the entire data set of
3706 independent reflections residual values are R = 0.0461 and Rw = 0.0789. The structure
was found to be isotypic to Pb9Pd13 with In and Sb on the Pb-sites.
The existence of a further ternary compound, which was already described as In4Pd3Sb2 could
be confirmed. It's composition range was determined by EPMA to be In1.2-1.3PdSb0.8-0.7. It
does not melt congruently and we were not able to find suitable single crystals. However, we
succeeded to prepare the pure ternary compound in order to perform X-ray powder diffraction
using a Guinier image plate technique. The entire diffraction spectrum was refined by Full
profile Rietveld method using the program Fullprof. The PdSn2 structure type (space group:
I41/acd; Pearson symbol: tI48, Z = 16), proposed for this compound, was confirmed and the
lattice parameters are a = 6.435(0) Å and c = 24.364(2) Å. The residual values were Rp =
5.34 and Rwp = 6.70. The tetragonal PdSn2-structure-type is a mixed variant of the CaF2-type
and the CuAl2-type structure. The free z-parameter of the 16d-position was found to be
significantly different as compared to that of PdSn2. However, calculations of powder patterns
for the original PdSn2 with our refined z-parameter agree much better with the observed
intensities reported in literature. Due to the long c-axes of the unit cell small changes of the zparameter result in a strong variation of the intensities of the diffraction pattern. Also in this
ternary compound we considered a random contribution of In and Sb over the 16e- and 16fpositions.
The electronic structures of both compounds were investigated by extended Hückel
calculations. Crystal Orbital Overlap populations show extended bonding interactions
between the main group elements. The bonding interactions of the main group elements are
almost optimized at the experimentally observed In/Sb ratio of the ternary compound. The
In/Sb ratio in In5.25Pd13Sb3.75 can thus be rationalized based on the electronic structure.
Nonstoichiometry and Defect Mechanism in Intermetallics
with L12-Structure
Herbert Ipser, Olga P. Semenova, Regina Krachler, Agnes Schweitzer, Wenxia Yuan1,
Ming Peng1, and Zhiyu Qiao1
(Inst. f. Anorganische Chemie, Universität Wien, Währingerstraße 42, A-1090 Wien, Austria;
1
Dept. of Physical Chemistry, Univ. of Science and Technology Beijing, P.R. China 100083)
Mat. Res. Soc. Symp. vol. 646 (2001), N6.11.1
A statistical-thermodynamic model was derived which allows to describe thermodynamic
activities in intermetallic compounds with L12-structure as a function of composition and
temperature. The energies of formation of the four types of point defects (anti-structure atoms
and vacancies on both sublattices) were used as adjustable parameters. The model was applied
to the three compounds Ni3Al, Ni3Ga, and Pt3Ga, and it permitted to estimate for the first time
the defect formation energies for Ni3Ga and to provide initial estimates for Pt3Ga.
Energetics of Point Defect Formation in Ni3Al
Hannes Schweiger*, Olga Semenova, Walter Wolf*, Wolfgang Püschl**, Wolfgang
Pfeiler**, Raimund Podloucky* and Herbert Ipser
(Institut für Anorganische Chemie and *Institut für Physikalische Chemie, University of
Vienna, Währingerstraße 42, A-1090 Vienna, Austria, and **Institut für Materialphysik,
University of Vienna, Strudlhofgasse 4, A-1090 Wien, Austria)
Scripta Mater. 46 (2002), 37
The energies required for creating vacancies and anti-site defects in L12-ordered Ni3Al are
calculated by ab-initio approaches. Based on a statistical-thermodynamic model, the thermodynamic activities of both components as a function of temperature and composition can be
derived using these defect formation energies as input parameters. A comparison of the
calculated activity curves with experimentally measured values demonstrates the high
reliability of the ab-initio approach to defect formation energies. The importance of some
computational options to obtain accurate results is discussed.
Intermetallic Phases with D03-Structure: A StatisticalThermodynamic Model
Herbert Ipser, Olga Semenova, and Regina Krachler
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
J. Alloys Comp. 338 (2002), 20
A statistical-thermodynamic model for binary nonstoichiometric D03-phases has been
developed based on a mean-field approximation. The corresponding D03 crystal lattice is
divided into three sublattices, the -, ß- and -sublattices, where A-atoms occupy the - and
-sublattices, and B-atoms occupy the ß-sublattice in the perfectly ordered case. Neglecting
interstitial defects, all other possible point defects, i.e. anti-structure atoms and vacancies on
all three sublattices are considered. Based on a grand-canonical approach the expressions for
the defect concentrations are derived as functions of composition and temperature, and from
these the thermodynamic activities of the two components can be calculated using energies of
formation of the six types of point defects as parameters. The model equations are applied to
the two intermetallic phases Fe3Al (at 500 K) and Ni3Sb (at 1200 K).
The Nonstoichiometric -Ni2In Phase with B82-Structure:
Thermodynamic Modeling
Peter Waldner1 and Herbert Ipser2
(1 Institut für Physikalische Chemie, Montanuniversität Leoben, A-8700 Leoben, Austria,
2
Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Intermetallics 10 (2002), 485
The Gibbs energy of the intermetallic -Ni2In phase with B82-structure in the system indiumnickel was modeled as a function of temperature and composition between 298 K and the
liquidus temperatures and at a total pressure of 1 bar. A three-sublattice approach was chosen
to account for the B82-structure. All available experimental thermodynamic information as
well as data about phase equilibria with neighboring phases were applied to optimize the
adjustable quantities of the model. Simultaneously the Gibbs energy functions of five adjacent
phases were optimized, and analytical expressions for the nickel-rich solid solution, the liquid
phase and three intermetallic compounds are presented as well. The gas phase was treated as
thermodynamically ideal. All calculations were performed using ChemSage.
The Binary System In-Ir: A New Investigation of Phase
Relationships, Crystal Structures and Enthalpies of Mixing
Hans Flandorfer, Klaus W. Richter, E. Hayer, Herbert Ipser1, G. Borzone2, and J.-P. Bros3
(1 Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria, 2 Department of Chemistry and Industrial Chemistry, University of Genova, 3 IUSTI,
University of Provence, F-13493 Marseille)
J. Alloys Comp. 345 (2002), 130
The In-Ir phase diagram was investigated by means of X-ray diffraction, electron probe
microanalysis and thermal analysis. The existence of the two intermetallic compounds In3Ir
and In2Ir was confirmed, and it was found, that In3Ir transforms into a low-temperature
modification In3Ir-LT (CFe3-type structure, oP16, Pnma) at temperatures below about 350 °C.
The peritectic decomposition reaction of In3Ir and In2Ir at 981 °C and 1188 °C, resp., were
confirmed. There are no indications of a liquid miscibility gap as suggested earlier in the
literature. On the other hand, some of the experimental results point to the existence of a
metastable high-temperature phase In54Ir46. Enthalpies of mixing were determined by hightemperature drop-calorimetry between 1190 and 1390 °C. The minimum in the extrapolated
enthalpy of mixing curve is about -18 kJ mol-1 at a composition slightly above xIr = 0.5.
Thermodynamic Modeling of the System Ni-In
Peter Waldner1 and Herbert Ipser2
(1 Institut für Physikalische Chemie, Montanuniversität Leoben, A-8700 Leoben, Austria,
2
Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Z. Metallkd. 93 (2002), 825
The complete nickel-indium system was thermodynamically assessed at a total pressure of
1 bar from room temperature up to liquidus temperatures. The Gibbs energies of five
condensed solution phases and five stoichiometric compounds were modeled using all
available T–x phase diagram and thermodynamic data. For the Ni-rich solid solution with
face-centered cubic structure as well as the liquid phase a substitutional approach was chosen
to describe the Gibbs energies. Sublattice models were applied to account for the description
of the thermodynamics of three nonstoichiometric intermetallic compounds. Three sublattices
were chosen according to the crystallographic structures of the -Ni2In and ’-Ni13In9 phases,
whereas two sublattices were selected for the -NiIn phase. The gas phase was treated as
thermodynamically ideal. All computations were carried out with the Gibbs energy
minimization program ChemSage and its routine for parameter optimization.
Correlations in the Arrangement of Anti-Structure Point
Defects in Intermetallic Phases with B2-(CsCl)-Structure
Regina Krachler and Herbert Ipser
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Phil. Mag. A 82 (2002), 3013
Based on the Bragg-Williams approximation, a statistical-thermodynamic approach is presented for
nonstoichiometric binary B2-phases with a pure anti-structure-defect mechanism. Whereas in the
original Bragg-Williams model only the state of long-range order is considered and no correlations are
allowed in the arrangement of the point defects, short-range order is introduced as an equilibrium
property of the system in the present work. This new approach is applicable both to highly ordered
intermetallic compounds as well as to completely disordered alloys, but is also applicable in the region
of the order-disorder transition. The obtained phase boundary which describes the order-disorder
transition is in good agreement with the results predicted by Monte Carlo calculations.
Estimation of Defect Formation Energies in the D019Intermetallic Compound Ti3Al
Olga Semenova, Regina Krachler, and Herbert Ipser
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Solid State Sci. 4 (2002), 1113
A statistical-thermodynamic model for binary nonstoichiometric intermetallic A3B
compounds with D019-structure was developed based on a mean-field approximation.
Vacancies and anti-structure atoms are allowed on the two sublattices as possible point
defects. Due to the identical stoichiometry and the analogous coordination around A and B
atoms it turned out that the same approach is valid as for A3B compounds with L12-structure,
and identical expressions were obtained, both for the concentrations of the different point
defects and for the thermodynamic activities. The energies of formation of the four types of
point defects were used as parameters. The model equations were applied to the intermetallic
compound Ti3Al using experimental aluminum activities from the literature. By a simple
curve fitting procedure the following defect formation energies were obtained: Ef(VTi) =
Ef(VAl) = 1.5 eV, and Ef(TiAl) = Ef(AlTi) = 0.6 eV. This results in very low vacancy
concentrations which means that the thermal disorder and the deviation from stoichiometry in
Ti3Al is caused almost entirely by anti-structure atoms. Their concentrations (referred to the
total number of lattice sites) are found to be about 0.0009 at 1123 K, i.e. 0.12 % of the Ti sites
are occupied by Al atoms and 0.36 % of the Al sites by Ti atoms.
Contact Materials for GaSb and InSb: A Phase Diagram
Approach
Klaus W. Richter and Herbert Ipser
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Acta Metal. Sinica (English Letters) 15 (2002), 143
Thermodynamic Factor in Diffusion in the Nonstoichiometric Compounds Ni3Ga and Pt3In
W. Yuan1, X. Wu1, Z. Qiao1, and Herbert Ipser2
(1 Department of Physical Chemistry, University of Science and Technology Beijing, China,
2
Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Rare Metals 21 (2002), 186
Thermodynamic Assessment of the Ni-Ga System
W. Yuan1, Herbert Ipser2, and Z. Qiao1,
(1 Department of Physical Chemistry, University of Science and Technology Beijing, China,
2
Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Beijing Keji Daxue Xuebao 24 (2002), 383
The Al-Ni-Si Phase Diagram between 0 and 33 at.% Ni
Klaus W. Richter and Herbert Ipser
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Intermetallics 11 (2003), 101
Fine Structure of the Melting Process in Pure CdTe and in
CdTe with 2 mol% of Ge or Sn
L. Shcherbak1, P. Feychuk1, O. Kopach1, O. Panchuk1, E. Hayer2, H. Ipser2
(1 Institut für Anorganische Chemie, Universität Chernivtsi, vul. Kotsibinskoho 2,
UA-58012 Chernivtsi, Ukraine, 2 Institut für Anorganische Chemie, Universität Wien,
Währingerstr. 42, A-1090 Wien, Austria)
J. Alloys Comp. 349 (2003), 145
The melting process of pure CdTe as well as of CdTe + 2 mol% Ge and CdTe + 2 mol% Sn
was investigated experimentally by means of differential thermal analyses. The samples were
heated above their respective melting temperatures Tm and annealed at various defined
temperatures before continuation of heating. Volume fractions of clusters, remaining in the
melt even above the melting point, were derived from the area of the corresponding thermal
effects. It was confirmed that the melt consists in all cases of two types of structures: clusters
(with a short-range order close to the crystalline substance) within an amorphous matrix. The
size of the clusters was estimated from the activation energies of the crystallization process;
they were found to consist of about 66 to 98 atoms in pure molten CdTe. For two cases, pure
CdTe and CdTe + 2 mol% Ge, “hot crystallization” was observed, i.e. after a given heat
treatment the melt crystallized at temperatures above Tm.
Pd as a Contact Material for InSb Semiconductors – the InPd-Sb Phase Diagram
Ch. Luef, H. Flandorfer, Klaus W. Richter, and Herbert Ipser
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
J. Electron. Mater. 32 (2003), 43
Fractional Site Occupation of Hf5-xNbxGe4: Crystallographic
Investigation and Thermodynamic Modeling
Klaus W. Richter1, Radim Picha1, Herbert Ipser1, and Hugo F. Franzen2
(1 Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria, 2 Ames Laboratory and Department of Chemistry, Iowa State University, Ames IA,
USA)
Solid State Sci. 5 (2003), 653
Structural Investigation of Ternary RIr3B2 Compounds (R =
Ce and Pr)
Oksana Sologub1, C. Rizzoli2, P. Salamakha3, and Herbert Ipser1
(1 Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria, 2 Dipartimento di Chimica GIAF, Universitá degli Studi di Parma, I-43100 Parma,
Italy, 3 Departimento de Quìmica, Instituto Tecnològico e Nuclear, P-2686-953 Sacavèm,
Portugal)
J. Alloys Comp., accepted (2003)
Structural studies were performed for the ternary RIr3B2 compounds (R = Ce and Pr) from as
cast samples. The crystal structure of the ternary boride CeIr3B2 (CeCo3B2 structure type,
space group P6/mmm, a=5.520(3) Å, c=3.066(2) Å, Z=1, V=80.91 Å3, x=15.154 g cm-3) was
refined to R1=0.0470, wR2=0.1240 from single crystal X-ray diffraction data. The new
ternary boride PrIr3B2 was found to be isostructural with the CeIr3B2 compound. Is lattice
parameters a=5.5105(2) Å, c=3.1031(1) Å were obtained from a Rietveld refinement of X-ray
powder diffraction data.
Crystal Structure and Physical Properties of Ternary
Compounds RPt3B (R = La, Pr, Nd)
Oksana Sologub1, Kurt Hiebl2, P.S. Salamakha3, and Herbert Ipser1
(1 Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria, 2 Institut für Physikalische Chemie, Universität Wien, Währingerstr. 42, A-1090
Wien, Austria, 3 Departimento de Quìmica, Instituto Tecnològico e Nuclear, P-2686-953
Sacavèm, Portugal)
J. Alloys Comp., accepted (2003)
The crystal structure of a new series of ternary rare-earth platinum borides RPt3B (R=La, Pr,
Nd) has been studied by X-ray powder diffraction analyses from the “as-cast” alloys. The
tetragonal RPt3B structure type, space group P4mm (No. 99), has been confirmed for all
compounds. Rietveld refinements for the two compounds, PrPt3B and NdPt3B, were
performed. LaPt3B is a temperature independent Pauli paramagnet from room temperature
down to 4 K. PrPt3B orders antiferromagnetically at TN = 15 K followed by a ferromagnetic
spin flip at TC = 5 K, whereas NdPt3B exhibits an antiferromagnetic spin alignment at a Néel
temperature TN = 7 K. The temperature dependence of the electrical resistivity, (T),
resembles the metallic character of these compounds. Furthermore the characteristic changes
of slope of (T) plots prove the magnetic transitions.
Thermodynamic Assessment of the Ni-Ga System
W.X. Yuan1, Z.Y. Qiao1, and Herbert Ipser2
(1 University of Science and Technology Beijing, 30 Xueyuan Lu, Beijing 100083, China,
2
Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
J. Phase Equil., accepted (2003)
Phase diagram and thermodynamic properties of the Ni-Ga system are assessed based on the
CALPHAD approach, using all available experimental data and applying appropriate
thermodynamic models. The liquid phase and the Ni-based solid solution (Ni) are treated as
disordered solutions. The thermodynamic behavior of the ordered intermetallic compounds
with appreciable ranges of homogeneity, Ni3Ga and NiGa, are described by a two-sublattice
model, and the order-disorder transformation between Ni3Ga and fcc-(Ni) is also explicitly
considered in this work. The other five intermetallic compounds are treated as stoichiometric
line compounds. The phase diagram and the thermodynamic properties calculated from the
optimized model parameters are in good agreement with most of the experimental data.
Lead-free Solder Materials
Christoph Luef, Hans Flandorfer, and Herbert Ipser2
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Z. Metallkd., submitted (2003)
The partial and integral enthalpies of mixing of molten, ternary Ag-Cu-Sn alloys were
determined at 500, 700 and 900°C using a Calvet type micro calorimeter. Five sections in a
compositional range from pure Sn to about 40 at.% Sn were investigated. The data were fitted
using a Redlich-Kister-Muggiano polynomial, where the binary interaction parameters were
taken from the literature. Additionally, the temperature dependence of the ternary interaction
parameters was described analytically by a linear function.
In the ternary Cu-Ni-Sn system, the enthalpies of mixing were determined at 1250°C in five
sections starting from pure Sn to about 40 at.% Sn. Again, the ternary interaction parameters
were fitted using the substitutional Redlich-Kister-Muggiano model. For both ternary systems
and all mentioned temperatures isoenthalpy curves were constructed for the integral molar
enthalpy of mixing. The experimental results of the ternaries were compared with calculated
values obtained by employing different binary extrapolation models.
Ni, Pd, or Pt as Contact Materials for GaSb and InSb
Semiconductors: Phase Diagrams
Herbert Ipser and Klaus W. Richter
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
J. Electron. Mater. accepted (2003)
As processing and even use of semiconductor devices usually includes the exposure to
elevated temperatures, interface reactions often occur, especially during metallization and
further heat treatment. It is thus important to understand the corresponding phase equilibria of
the involved elements. We present here the phase diagrams of Ni, Pd, and Pt with GaSb and
InSb: experimental results in the systems Ga-M-Sb and In-M-Sb (M = Ni, Pd, Pt) are
summarized and are discussed in the context of contact chemistry. For GaSb and InSb it is
found that, from a thermodynamic point of view, binary and ternary compounds in
equilibrium with the corresponding semiconductor would be the best choice for contact
materials as these contacts will remain stable even after long exposure to elevated
temperatures.
Specific Heat Capacities of Alloys of the Nonstoichiometric
GaNi3x Phase
Hans Flandorfer and Herbert Ipser
(Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien,
Austria)
Intermetallics accepted (2003)
The heat capacities of three alloys, Ga0.24Ni0.76, Ga0.25Ni0.75, and Ga0.27Ni0.73, within the
homogeneity range of the nonstoichometric compound GaNi3x were determined between 423
and 1273 K. Two different methods, flat specimen DSC (423 – 1073 K) and drop calorimetry
(773 – 1273) were used and the overlap of the results was satisfying for all three compounds.
Cp-values start at about 26 -27 kJ.mol-1.K-1 (423 K), increase slightly up to 800 – 900 K and
rise strongly at higher temperatures. This behavior is not unusual for metals. Up to about 900
K the Neumann-Kopp rule is suitable to estimate the Cp-values. The only significant
difference between the three alloys is the weaker rise of Cp for Ga0.27Ni0.73 in comparison to
Ga0.24Ni0.76 and Ga0.25Ni0.75. The Cp-values at 1273 K are about 35 kJ.mol-1.K-1 for Ga0.27Ni0.73
and close to 40 kJ.mol-1.K-1 for the other two alloys. The experimental values could be fitted
by the least squares method using the polynomial Cp = a + b.T + c.T2. The widely used T-2term was not applied because it caused an unsatisfying approximation to our experimental
values at lower temperature (423 – 600 K). This can be explained by the lack of experimental
values at room temperature and slightly above. The extrapolated Cp-values at room
temperature, Cp(298), are close to 25 kJ.mol-1.K-1 for all three compounds.
On the Low Temperature Stability of In2Pt
Marta Patrone1), Klaus W. Richter2),Gabriella Borzone1) and Herbert Ipser2)
(1) Dipartimento di Chimica e Chimica Industriale ,Università di Genova, Via Dodecaneso 31,
I-16146 Genova, Italy, 2)Institut f. Anorganische Chemie, Universität Wien, Währingerstrasse
42, A-1090 Wien, Austria)
J. Alloys Comp. accepted (2003)
The low temperature stability of the phase In2Pt (Pearson symbol: cF12, Structure type CaF2)
was investigated by various annealing experiments and differential thermal analysis. It was
found that the eutectoid decomposition of In2Pt at 674 °C reported earlier does not exist and
that the phase In2Pt is stable with respect to decomposition into the neighboring phases In7Pt3
and In3Pt2 down to a temperature of at least 400 °C.
Thermodynamic Investigations in the Lanthanum-Cadmium
System
Klaus W. Richter1),Sonia Besana2), Gabriella Borzone2) and Herbert Ipser1)
(1)Institut f. Anorganische Chemie, Universität Wien, Währingerstrasse 42, A-1090 Wien,
Austria, 2) Dipartimento di Chimica e Chimica Industriale ,Università di Genova, Via
Dodecaneso 31, I-16146 Genova, Italy)
J. Alloys Comp. accepted (2003)
An isopiestic vapor pressure method was developed which allows vapor pressure
measurements in systems containing elements that are air and/or moisture sensitive. With this
method, cadmium vapor pressures were determined for the intermetallic compound La13Cd58
and the neighboring two-phase field with LaCd2 between about 750 and 1020 K. From these,
activities and partial molar enthalpies were derived, and integral Gibbs energies of formation
were obtained by a Gibbs-Duhem integration. It was found that the compound La13Cd58
shows some non-stoichiometry extending between about 79 and 81.5 at% Cd. The enthalpy of
formation of La13Cd58 was determined by a calorimetric method; it was found to be
H298 = -32.0±2.0 kJ mol-1.
Triple-defect Complexes in the B2 Intermetallic Compound
NiAl
Regina Krachler and Herbert Ipser
(Institut f. Anorganische Chemie, Universität Wien, Währingerstrasse 42, A-1090 Wien,
Austria)
Phys. Rev. B submitted (2003)
Near the stoichiometric composition and at temperatures far below the critical temperature of
order-disorder, the three classical mean-field statistical-thermodynamic models for
intermetallic phases, the Wagner-Schottky approach, the Bragg-Williams approach, and the
Bethe-Bragg-Williams approximation, yield practically identical results for the
thermodynamic expressions. However, only the Bethe-Bragg-Williams approximation is able
to describe the equilibrium concentrations of point defect complexes. The present study
combines a theoretical model on the basis of the Bethe-Bragg-Williams approximation with
literature data on the pair-interaction energies in ’-NiAl with B2- (CsCl-) structure. In this
compound, the most interesting point defect complexes are the triple-defects, since they have
been supposed to be mainly responsible for the concentration dependence of the Ni selfdiffusion coefficient in the temperature range between 1000 and 1300 K which is nearly
constant for Al-rich and stoichiometric alloys and shows a pronounced increase with
increasing Ni content on the Ni-rich side of the composition range. The theoretical
composition dependence of the triple-defect complex concentration, derived in the present
work, and the experimental Ni diffusivities from the recent literature show excellent
correlation, thus pointing to an important contribution of the triple defect diffusion
mechanism in B2 NiAl.
Thermodynamics and Nonstoichiometry in the Intermetallic
Compound Pt3In
Agnes Schweitzera, Xiaohong Wub, Wenxia Yuanb, Yongzhang Huanga, Jens Dischingerc,
Hans-Jürgen Schallerc, Zhiyu Qiaob, Friedrich Gehringera, and Herbert Ipsera
(a Institut für Anorganische Chemie, Universität Wien, A-1090 Wien, Austria, b Dept. of
Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, P.R.
China, c Institut für Physikalische Chemie, Universität Kiel, D-24118 Kiel, Germany)
Intermetallics submitted (2003)
Thermodynamic activities of indium were measured between 973 and 1273 K in the
nonstoichiometric intermetallic compound Pt3In using an emf-method based on an oxygen
conducting solid electrolyte. The variation of the lattice parameter with composition was
determined by powder X-ray diffraction, and the corresponding results point to a considerably
wider homogeneity range on the indium-rich side than previously reported. The results of the
activity measurements are interpreted in terms of a statistical-thermodynamic model for L12phases considering four types of point defects, i.e. anti-structure atoms and vacancies on the
platinum and indium sublattices. The energies of formation of the point defects at the
stoichiometric composition are estimated from a curve fitting procedure yielding the
following set of values: Ef(PtIn) = Ef(InPt) = 1.15 eV, EfV(Pt) = EfV(In) = 2.0 eV. This results
in a disorder parameter ‘ = 5·10-6 at 1173 K which means that at the stoichiometric
composition 0.002 % of the indium sublattice sites are occupied by platinum atoms and
0.0007 % of the platinum sites by indium atoms at this temperature.