Al-rich region of Al-Pt

Article abstract of DOI:10.1016/j.jallcom.2013.07.178

The constitution of the Al-rich part of the Al Pt alloy system is revised. Apart from the previously reported equilibrium Al4Pt, Al21Pt8 and Al2Pt phases, a complex intermetallic was revealed at 75- 76 at.% Al between 801 and 915 °C. Its structure determined by electron diffraction is orthorhombic (Bmmb, a = 1.983, b = 1.636 and c = 1.422 nm).

Full text of DOI:10.1016/j.jallcom.2013.07.178

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Al-rich region of Al−Pt
B. Grushko, D. Kapush, J. Su, W. Wan, S. Hovmöller
PII:
S0925-8388(13)01803-3
DOI:
http://dx.doi.org/10.1016/j.jallcom.2013.07.178
JALCOM 29102
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26 July 2013
Please cite this article as: B. Grushko, D. Kapush, J. Su, W. Wan, S. Hovmöller, Al-rich region of Al−Pt, (2013),
doi: http://dx.doi.org/10.1016/j.jallcom.2013.07.178
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Al-rich region of Al−Pt
B. Grushko a, D. Kapush b, J. Suc, W. Wan c, S. Hovmöller c
a PGI-5, Forschungszentrum Jülich, 52425 Jülich, Germany
b Dept. Physical Chemistry of Inorganic Materials, I.N. Frantsevich Institute for Problems of
Materials Science 03680 Kyiv 142, Ukraine
c Dept. Structural Chemistry MMK, Stockholm University,10691 Stockholm. Sweden
Abstract
The constitution of the Al-rich part of the Al−Pt alloy system is revised. Apart from the previously
reported equilibrium A14Pt, A121Pt8 and Al2Pt phases, a complex intermetallic was revealed at
75-76 at.% Al between 801 and 915 °C. Its structure determined by electron diffraction is
orthorhombic (Bmmb, a = 1.983, b = 1.636 and c = 1.422 nm).
Keywords: A. Transition metal alloys and compounds; C. Phase diagrams.
---------------------------
 Corresponding author. Tel: +49 2461 612399; fax: +49 2461 616444.
E-mail address: b.grushko@fz-juelich.de (B. Grushko).
1

1. Introduction
The information on the constitution of the Al−Pt alloy system published up to 1983 was reviewed
in Ref. [1], where some items are classified as problematic. The high-Al part of the phase diagram
assessed there and containing the congruent Al3Pt2 phase (melting point 1527 °C) and three higher-Al
intermetallics formed by a cascade of peritectics is based on the data from Ref. [2]. The A12Pt phase is
formed from Al3Pt2 and the liquid at 1406 °C, A121Pt8 from Al2Pt and the liquid at 1127 °C, and
A121Pt5 from Al21Pt8 and the liquid at 806 °C1. Finally, the L ↔ A121Pt5 + (Al) eutectic reaction takes
place at 657 °C close to the Al terminal.
The highest-Al phase was concluded in Ref. [2] to be cubic (a = 1.923 nm) of the Al4Pt or A121Pt5
composition. In hypereutectic alloys a hexagonal phase (a = 1.302, c = 0.961 nm) of rather A121Pt6
composition was reported in Ref. [3], where it was found to transform into the above-mentioned cubic
A121Pt5 phase over a period of several hours at 200 °C. Only a hexagonal phase was revealed later in
Ref. [4] in samples containing 19-21 at.% Pt and annealed for two days at 597 °C. Its most probable
composition was concluded to be Al4Pt and the lattice parameters determined were very close to those
of A121Pt6 in Ref. [3]. In spite of this, the metastability of the latter was assumed in Ref. [1] and cubic
A121Pt5 indicated in the accessed phase diagram. More recently, this question was studied again in Ref.
[5], where the phase at Al4Pt was found to be rhombohedral (P3c1, a = 1.3077, c = 0.96342 nm ) and
isostructural with Al4Pd. According to the structural model of Ref. [5] the phase contains 20.25 at.% Pt.
Apart from Al4Pt (λ-phase) also A121Pt8 (γ-phase) and A13Pt2 (δ-phase) exhibit structures similar to
those of the phases formed in Al−Pd at the same Al concentrations (see Table 1; for Al−Pd see Ref. [6]
and references therein).
The discovery of quasicrystals in rapidly solidified Al−Mn alloys inspired similar studies also on
Al−Pt. Electron diffraction investigation of a rapidly solidified Al5Pt alloy in Ref. [7] did not reveal
quasicrystals, but a complex hexagonal phase (a = 1.231, c = 2.623 nm) was reported. The latter was
found to be similar to an Al5Ir hexagonal phase and structurally related to a decagonal phase. In both
Al−Ir and Al−Pt, these structures were concluded to be metastable, since they disappeared in annealed
samples [7]. Such a hexagonal structure was also reported in Ref. [8], where an alloy formed by
diffusion between thin layers of Al and Pt (overall composition close to Al9Pt) was studied by electron
diffraction. On the other hand, a more detailed investigation of the Al−Ir alloy system identified the
above-mentioned “Al5Ir” structure as the stable rhombohedral χ-Al28Ir9 phase (i.e. stable at somewhat
1 The temperatures 1521, 1406, 1121 and 806 °C are mentioned in Ref. [2].
2

different composition, see Ref. [9] and references therein). In Ref. [10] a similar stable χ-phase was
revealed in Al−Ni−Pt alloys (see Table 1), where this finding was interpreted as a ternary stabilization
of a binary Al−Pt χ-phase. The latter was assumed to be metastable based on the conclusions of Ref. [7,
8], i.e. without experimental verification of the relevant region of the Al−Pt phase diagram. The
stabilization effect of Ni was also assumed for the ε6-phase (belonging to the εi family) revealed in
Al−Ni−Pt in Ref. [10] at close Al concentration. While such a structure was not observed in Al−Pt, it is
stable around the Al21Pd8 composition at elevated temperatures (see Ref. [6]).
In the present work neither the Al−Pt χ-phase nor εi-phase was confirmed to be stable, but another
stable structure was revealed to be formed at elevated temperatures between the Al4Pt and A121Pt8
compositions.
Subsequently, the Al−Pt phase diagram was reinvestigated between 65 and 100 at.% Al.
2. Experimental
Initial alloys of ~2 g were produced by levitation induction melting in a water-cooled copper
crucible under a pure Ar atmosphere. The purity of Al was 99.999 % and of Pt 99.5 %. Additional
alloys of intermediate compositions were produced by mixing of residuals of the previously studied
samples. Parts of the solidified ingots inserted into the Al2O3 crucibles were thermally annealed under
argon atmosphere at 1100 °C and under vacuum at lower temperatures for up to 280 h. For rapid
heating of samples the furnace and sample holder with an empty alumina crucible were heated to a
preset temperature, then the holder was quickly removed and returned to the furnace with the samples.
The samples were subsequently water quenched.
Differential thermal analysis (DTA) examinations were carried out in alumina crucibles under the
pure He atmosphere up to 1450 °C at heating and cooling rates of 5 to 50 K/min. The Al and Au
standards were used to verify the temperatures measured by DTA. In several experiments these
standards were placed in the reference crucible, so the thermal effects of their melting and
solidification appeared in the corresponding plots of the studied alloys. The as-cast and thermally
annealed alloys were studied by powder X-ray diffraction (XRD) and scanning electron microscopy
(SEM). The local phase compositions were determined in SEM by energy-dispersive X-ray analysis
(EDX) on polished unetched cross sections. Powder XRD was carried out at room temperature in the
transmission mode using Cu K1 radiation and an image plate detector.
3

The samples for transmission electron microscopy (TEM) examinations were dispersed in absolute
ethanol and treated in an ultrasonic bath for 5 minutes. A droplet of the suspension was transferred
onto a carbon-coated copper grid and dried in air before the TEM observation. The rotation electron
diffraction method (RED) [11] was used, which allowed almost all the three-dimensional (3D) electron
diffraction data to be collected by combining the electron beam tilt and the goniometer tilt. RED was
carried out on a JEOL JEM-2100 microscope operated at 200 kV using a single-tilt tomography
sample holder. 3D RED data collection was automatically controlled by the RED data collection
software package [12]. In total, 1470 electron diffraction frames were collected in 2 h covering a tilt
range from -70.82 to 70.01 ° (i.e. with only 39.17° missing cone) with a step size of 0.10 °. The
exposure time for each electron diffraction frame was 0.5 s. The data completeness is 100% up to a
resolution of 0.07 nm. Using RED the three-dimensional reciprocal lattice was reconstructed, and unit
cell, space group and intensities were obtained.
3. Results and Discussion
3.1. Phases Al2Pt, A121Pt8 and A14Pt
SEM/EDX examinations of as-cast alloys containing 10-30 at.% Pt only revealed the phases whose
compositions were close to the stoichiometries of Al2Pt, A121Pt8 and A14Pt exposed in the phase
diagram of Ref. [1]. The morphologies of the solidified phases were consistent with their peritectic
formation and the formation of an eutectic close to the Al terminal (see examples in Fig. 1.).
The powder XRD pattern of an as-cast sample containing 33 at.% Pt (Fig. 2a) was successfully
indexed according to the crystallographic data known for Al2Pt (see Table 1), and a DTA examination
revealed its (peritectic) melting at ~1405 °C, i.e. in agreement with the literature data.
Powder XRD of a sample of 27.5 at.% Pt annealed at 1100 °C (Fig. 2b) confirmed the structure
associated with the γ-phase (see Table 1). DTA examinations of samples with this and somewhat
higher or lower Pt concentrations (see Fig. 3a,b, for example) revealed the melting of the γ-phase at
temperatures ranging between 1124 and 1131 °C, which is close to that of the A12Pt  L + γ reaction
in Ref. [1]. The single λ-phase was produced in a sample of 20 at.% Pt annealed at 780 °C. The
corresponding powder XRD pattern (Fig. 2c) was in good agreement with that calculated from the
structural model of Ref. [5]. The samples of 22-26 at.% Pt annealed at 780 °C consisted of the γ + λ
mixture and the compositions of the γ and λ phases measured by EDX were ~Al72Pt28 and ~Al80Pt20,
4

respectively. In samples containing Pt < 20 at.% the λ-phase of about the same composition was found
at 640 °C in equilibrium with (Al) dissolving very little Pt. These phases form the eutectic close to the
Al terminal.
With respect to the cubic A121Pt5 phase reported in Ref. [2], this formula was only mentioned as
more plausible than Al4Pt for the estimated 416 atoms per unit cell. Its powder XRD pattern
reproduced in Fig. 4a shows a great similarity to that of the rhombohedral λ (Fig. 4b), i.e. both
probably correspond to the same structure. No numerical data were presented in Ref. [2] and the cubic
structure of A121Pt5 is only preliminarily concluded. In a trial to confirm this, all the lines of a
diffraction pattern of λ collected in the present work were indexed using either the rhombohedral
lattice (P3c1, a = 1.3089(2), c = 0.9633(1) nm) or a primitive cubic lattice (a = 1.9257(7) nm) and the
result are compared in Appendix 1. After this refinement the average Δ(2θ) = 0.009 ° and FOM(30) =
19.2 were obtained for the rhombohedral and average Δ(2θ) = 0.060 ° and FOM(30) = 2.5 for the cubic
structure. The diffraction data of the hexagonal A121Pt6 phase of Ref. [3] plotted in Fig. 4c also show a
very similar pattern. In spite of differences in relative intensities, which could follow in Ref. [3] from
the preferred orientation of unidirectionally solidified materials, all three patterns could be associated
with one structure. The transformation of the hexagonal A121Pt6 structure to a cubic A121Pt5 structure
claimed in Ref. [3] remains unclear, since no diffraction data of the latter were supplied. Obviously,
the same rhombohedral A14Pt phase was also observed in Ref. [4].
Apart from the already mentioned formation temperatures of Al2Pt and γ, also the eutectic
temperature measured in our DTA experiments at 655 °C is close to that accepted in Ref. [1]. This
value was obtained from the examinations of samples annealed at 640 °C. Somewhat lower values of
the eutectic temperatures were frequently observed in solidified samples or those water quenched from
the solid-liquid state. This can be related to some supersaturation of (Al) in these materials. DTA of
samples containing the λ-phase revealed thermal effects at somewhat above 800 °C, i.e. corresponding
to the peritectic reaction λ  L + γ in Ref. [1], but additional details were revealed that required
further examinations.
3.2. New phase between A121Pt8 and A14Pt
In the heating plot of as-cast Al80Pt20 (Fig. 3b) the strong endothermic effects starting from 654,
827 °C and 1128 °C respectively could be associated with the (Al)-λ eutectic melting, the peritectic
melting of λ and the peritectic melting of γ mentioned in Ref. [1]. This alloy indeed consisted of the
5

primary γ-phase grains surrounded by the λ-phase, and the rest of the liquid solidified in a form of
eutectic (Fig. 1b). In a cooling plot of this alloy in Fig. 3c the temperature of 1174 °C can be associated
with the liquidus above the peritectic formation of γ at 1028 °C, then the peritectic formation of λ at
779 °C and finally the eutectic solidification follow. This cooling at 50 K/min resulted in a constitution
similar to that in the as-cast material, and the second heating DTA plot looked essentially the same as
the previous one. The temperature 827 °C (in other runs temperatures of up to 836 °C were recorded)
is somewhat higher than that assessed in Ref. [1] for the reaction λ  L + γ. Transition temperatures
much closer to 806 °C mentioned in Ref. [1] and even somewhat below this were revealed in samples
containing 22-26 at.% Pt (see Fig. 3d). An overheating of the λ-phase due to a delayed nucleation of
the γ-phase in Al80Pt20, as compared to that in Al76Pt24, could not be excluded, but this is not the most
plausible explanation, since the γ-phase was present initially in both of them. Moreover, a weak
additional effect appeared in the DTA plot of Fig. 3b starting from 816 °C. Also the plot in Fig. 3d
exhibited a duplet, but with a weaker second minimum. In another example in Fig. 3e the minima are
comparable.
In agreement with Ref. [1], the samples of 22-26 at.% Pt annealed at 780 °C consisted of the γ + λ
mixture (see Fig. 5a and Fig. 6a), in those annealed at 950-1100 °C the γ-phase of the same
composition was found in equilibrium with the liquid (see Fig. 5b). However, their annealing at 850-
900 °C revealed the formation of an additional phase of ~Al76Pt24. In Fig. 5c this is the major
constituent with some inclusions of the γ-phase, and Fig. 5d illustrates its coexistence with γ and λ
after cooling from 900 °C in a DTA experiment. Thus, being a high-temperature phase, already
unstable at 780 °C and below this, it remained in materials cooled at relatively low rates. Nevertheless,
in the following experiments the samples containing this phase were water quenched after annealing.
The existence of a new structure was confirmed by powder XRD (see Fig. 6b). The new phase,
designated ξ, exhibited a complex diffraction pattern, which was different from those of the suspected
phases χ (Fig. 6c) and ε6 (Fig. 6d). Its direct indexing was not achieved. Subsequent electron
diffraction examinations revealed an orthorhombic structure (Bmmb, a = 1.983, b = 1.636 and c =
1.422 nm). The typical electron diffraction patterns are presented in Fig. 7. Using these lattice
parameters, it was attempted to index the powder XRD pattern of the ξ-phase in order to obtain a
temporary standard (see Appendix 2). The structural determination of the Al−Pt ξ-phase is in progress.
6

3.2. Transition temperatures
The incorporation of the ξ-phase in the phase diagram requires three new reactions instead of L + γ
↔ λ as claimed in Ref. [2] at 806 °C (see broken line in Fig. 8). The above-mentioned coexistence of
the γ-phase with the liquid at 950 °C and with the ξ-phase at 900 °C indicated an L + γ ↔ ξ reaction
between these temperatures. At still lower temperatures the reactions L + ξ ↔ λ and ξ ↔ γ + λ are
expected.
The determination of the temperatures of the three reactions involving the ξ-phase was not
straightforward. In regular DTA experiments of relevant samples heating plots indicated phase
transitions in a range of 800-835 °C and at ~1127 °C, but no additional effects between these limits
were detected (see Fig. 3b). Also in the corresponding cooling plots no thermal effects were associated
with the formation of the ξ-phase (see Fig. 3c), and the ξ-phase was not revealed in these samples
examined after DTA. Therefore, a series of annealed-and-quenched Al80Pt20 samples were examined by
SEM/EDX and powder XRD. This composition was selected expecting to obtain liquid-solid equilibria
in a wide temperature range.
Samples annealed for 20-65 h at and sharply quenched from 850-900 °C contained major ξ and a
visible liquid fraction. Then they were quickly inserted into a furnace preheated sequentially to several
temperatures ranging from 780 to 950 °C, annealed for different times and then water quenched. At
780 °C the complete transformation of the ξ-phase was already achieved after 6 min. The sample
contained essentially single λ. This means that in regular DTA experiments no ξ-phase could survive
during heating up to ~800 °C (i.e. the lowest observed by DTA transition temperature). However, such
a transformed ξ-phase was found to recover completely after annealing of the previous sample at 855
°C for one hour. The same annealing of an as-cast sample of this composition, containing a visible
fraction of γ, resulted in only partial equilibration, so both ξ and γ were revealed there. The complete
decomposition of the ξ-phase was also achieved by annealing at 950 °C for one hour. Shorter
annealing times were not tested. The corresponding quenched sample contained coarse grains of γ and
solidified liquid, similarly to that when it was heat treated from the as-cast initial state. However, the
initial ξ-phase annealed at 930 °C for an hour or at 915 °C for three hours remained untransformed.
Moreover, annealing of initial λ at 915 °C for three hours resulted in the formation of ξ+L. In order to
specify the temperature of the suggested L + γ ↔ ξ reaction, previously studied samples containing
either ξ+sL or γ+sL (sL = solidified liquid) were inserted together into a furnace preheated to 915 °C.
After 42 h annealing and quenching it was not possible to separate them without destroying, but the
regions of initial samples could still be well identified. Both initial grains of either γ-phase or ξ- phase
7

remained untransformed, although the surrounding liquid exhibited continuity. The same sandwich
subsequently annealed at 930 °C for 18 h only contained γ+L. Therefore, the transition temperature is
probably close to 915 °C and it is conditionally accepted in the updated phase diagram (see Fig. 8).
Considering these results, DTA experiments with more complex thermal procedures were carried
out on Al80Pt20 containing initially ξ+sL. For example, after heating to 850-880 °C at 50 K/min
(maximal rate allowed by the DTA device used) the samples were kept at the existing temperatures of
the ξ-phase for up to 2 h and then further heated to 1200-1300 °C at 10-15 K/min. Examples of the
recorded DTA plots are shown in Fig. 9. In Fig. 9a in the first heating step the ξ-phase decomposed
with the formation of λ+γ (exothermal reaction starting from 530 °C), and then recombined starting
from 813 °C. In the second heating step the transformation of the recovered ξ-phase was already
revealed (see Fig. 9b,c, weak endothermic effects starting from 998 °C) prior to the peritectic melting
of γ, but the transition temperature was much higher than 915 °C estimated from the above-mentioned
annealing experiments. In Fig. 9c the plot of a sample of a lower Pt concentration additionally exhibits
eutectic melting.
The observation of the above-mentioned duplets (not always resolved) in the range of 800-836 °C
is consistent with the existence of two reactions at close temperatures: the lower-temperature thermal
effect could correspond to ξ ↔ γ + λ and the higher to L + ξ ↔ λ. The recombination of the ξ-phase
from γ + λ by heating could be more difficult if samples have a coarser structure, so in DTA
experiments higher transition temperatures are expected to be observed. Samples annealed at 780 °C
initially contained a coarser γ + λ mixture than those obtained by a decomposition of the initial ξ-
phase. Thus, the lowest temperature of 801 °C, observed in an Al76Pt24 sample annealed at and
quenched from 880 °C, can be associated with the reaction ξ ↔ γ + λ. The direct temperature
determination of the L + ξ ↔ λ reaction is complicated in these samples due to its small difference
from that of ξ ↔ γ + λ , while in Pt-poorer samples overheating is an obstacle.
In order to specify the temperature of the L + ξ ↔ λ reaction, an Al84.7Pt15.3 alloy was annealed in a
series of experiments for an hour in the DTA device at different temperatures between 812 and 837 °C
and then cooled down at 10 K/min. The samples cooled from 837 or 822 °C exhibited a well-resolved
endothermic effect associated with the formation of the λ-phase and then the effect of the eutectic
solidification. The former was very weak if the sample was cooled down from 817 °C, while the
sample cooled down from 812 °C exhibited only eutectic solidification. Therefore, 812 °C is already
below and 817 °C is close to the L + ξ ↔ λ transition. Due to some temperature variations around the
latter temperature the ξ-phase appeared and disappeared, so finally only a small fraction of this phase
8

was transformed by the subsequent cooling. Thus, the temperatures of 801 °C and 817 °C are accepted
in the phase diagram (Fig. 8).
3.4. Miscellaneous
A phase exhibited the same symmetry and close lattice parameters as those of the Al−Pt ξ-phase
reported here was earlier revealed in Al−Pd−Mn and designated there ξ (see Ref. [13] and references
therein). Therefore the same name was used for the new Al−Pt phase. The Al−Pd−Mn ξ was found to
coexist with another ternary phase designated ξ’. Both were concluded to be structurally related.
Particularly, the lattice parameters b of the ξ-phase and ξ’-phase are the same, while the lattice
parameter a of the ξ-phase is ~τ times larger than that of the ξ’-phase and the lattice parameter c is ~τ
times smaller (see Ref. [13], τ is the golden mean). While the stability of the Al−Pd−Mn ξ-phase was
doubted in Ref. [14], the ξ’-phase was found to be stable and to be actually a ternary extension of the
Al−Pd ε6-phase forming at elevated temperatures around the Al21Pd8 composition (see Ref. [6, 15] and
references therein). The Al−Pt ξ-phase is also expected to be similarly related to the Al−Pd ε6-phase.
Although neither of the phases of the εl-family was revealed in Al−Pt, the ε6-phase was found to be
stable in Al−Ni−Pt, which is in favor of its possible formation also in Al−Pt in metastable states [10].
The formation of metastable phases might be possible in Al−Pt by even relatively slow cooling
from the melt. In several (hardly reproducible) DTA experiments additional thermal effects were
observed at temperatures slightly below that associated with the γ-phase solidification. For example, in
the cooling plot in Fig. 10a the maximum starting from 1087 °C exhibited a “satellite” missing in most
of the other similar runs. Undercooling values of this reaction scattered in a significantly wider
temperature range than those of the λ-phase solidification. A DTA cooling plot in Fig. 10b already
exhibited a well-resolved exothermal effect starting from 945 °C. This could indicate the emergence of
an additional phase. The detected temperatures are much above the estimated temperature of the ξ-
phase stability. XRD examination of the corresponding samples after DTA only revealed λ and γ. As
follows from the previous experiments, the formation of the stable ξ-phase is quite sluggish, but once
formed it remained in the material cooled at reasonable rates, while the suspected additional metastable
phase did not survive during cooling at similar rates.
The formation of a metastable phase from the εi-family is not excluded. Indeed, in Ref. [8] the
structure of a metastable Al−Pt phase was suggested to be primitive tetragonal with a = 1.358 and c =
1.6646 nm, but this identification, based on electron diffraction examinations, was only supported by
the presentation of two diffraction patterns taken at high-index orientations. The above-mentioned c
9

value is typical of the b lattice parameters of all ε-s and ξ, while the a value is close to that of the (110)
line of ε6. Unfortunately, the data in Ref. [8] are not sufficient for more reasonable clarification. This
was definitely not the ξ-phase, whose peak list does not contain a value close to 1.358 nm.
Alternatively, the metastable phase, suspected of being formed in our experiments, might be the χ-
phase, resembling the second metastable phase reported in Ref. [8] and also that earlier described in
Ref. [7].
4. Conclusions
Present experiments confirmed the existence of the previously reported Al4Pt, A121Pt8 and A12Pt
phases. Apart from these also an additional stable phase was revealed at ~75-76 at.% Al, i.e. in a range
between those of Al4Pt and A121Pt8. Its temperature region of stability is between about 801 and
915 °C. The phase is orthorhombic (Bmmb, a = 1.983, b = 1.636 and c = 1.422 nm) and resembles the
Al−Pd−Mn ξ-phase.
Acknowledgements
The authors thank C. Thomas, E.M. Würzt and M. Kruth for technical contributions, and A. Kovács
and L. Meshi for helpful discussions. D.K. thanks Forschungszentrum Jülich for hospitality.
10

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11

Figure captions
Fig. 1. SEM metallography of: a) as-cast Al69.4Pt30.6, b) as-cast Al80Pt20, c) Al93Pt7 cooled in DTA from
1000 °C at 50 K/min. Here and below the nominal compositions of the alloys are given.
Fig. 2. Powder XRD patterns of: a) A12Pt in as-cast A167Pt33, b) A121Pt8 (γ) in A176Pt24 annealed at
1095 °C for 4 h, c) A14Pt (λ) in A180Pt20 annealed at 780 °C for 166 h,
Fig. 3. DTA plots of: a) as-cast Al69.4Pt30.6 (heating at 20 K/min), b) as-cast Al80Pt20 (heating at 20
K/min), c) Al80Pt20 (cooling at 50 K/min), d) Al76Pt24 annealed at 900 °C for 163 h (heating at 10
K/min), e) as-cast Al76Pt24 (20 K/min). The Al standard was inserted at the reference position,
therefore the thermal effect of its melting appeared in (e) with the opposite signs.
Fig. 4. Powder X-ray diffraction patterns (scaled according to 1/d2) of: a) the Al4Pt phase (also known
as A121Pt5) reproduced from Ref. [2] (scanned image), b) the λ-phase collected in the present work, c)
the A121Pt6 phase plotted from the diffraction data in Ref. [3].
Fig. 5. SEM metallography of: a) Al74.7Pt25.3 annealed at 780 °C for 166 h, b) Al78Pt22 annealed at
950 °C for 22 h, c) A176Pt24 annealed at 880 °C for 163 h, d) as above heated in DTA to 880 °C, held at
this temperature for an hour and cooled down to room temperature at 50 K/min.
Fig. 6. Powder XRD patterns of: a) γ + λ in A174.7Pt25.3 annealed at 780 °C for 166 h, b) ξ in A176Pt24
annealed at 880 °C for 18 h, c) χ in Al−Ni−Pt [10], d) ε6 in Al−Ni−Pt [10].
Fig. 7. Electron diffraction patterns of the ξ-phase (the 2D slices extracted from the 3D RED data) in
the: a) [001], b) [010] and c) [100] orientations. The red lines around the central spot represent the a*
direction, green the b* direction, and blue the c* direction (colors only shown in the online version).
Due to the rotation limitations the data inside the 39.2 ° reciprocal cone were not collected and,
subsequently, are missing in the 2D slices.
Fig. 8. Al-rich part of the Al−Pt constitutional diagram including the present results. The isotherm at
806 °C marked by the broken line corresponds to the equilibrium L + γ ↔ λ reported in Ref. [2] and
not confirmed in the present work.
12

Fig. 9. Two-stage heating DTA plots of: a,b) Al76Pt24 annealed at 850 °C for 18 h, and c,d) Al80Pt20
annealed at 900 °C for 261 h. After the first heating at 50 K/min to 850 °C the samples remained at this
temperature for up to 2 h and then heated up to 1300 °C at 10 K/min.
Fig. 10. Selected DTA plots by cooling from 1300 °C (50 K/min) of: a) Al80Pt20, b) Al76Pt24. The Al or
Au standard was inserted at the reference position, therefore the thermal effects of their solidification
appeared in the plots with the opposite signs.
13

Table 1. Crystallographic data for the phases mentioned in the text (ED = electron diffraction data).
Phase
λ-Al4Pt
ξ
S.G.
Lattice parameters
Comment
a, nm
b, nm
c, nm
P3c1
1.3077
1.3089(2)
2.032
-
-
0.96342
0.9633(1)
1.476
1.422
1.0684
1.0659(1)
-
[5]
This work
[13], Al−Pd−Mn, ED
This work, ED
[4]
This work
Al68Pt32 [4]
This work
[8], metastable, ED
[10] Al74Ni7.2Pt18.8
[13], Al73.5Pd22.4Mn4.1
[10] Al73Ni10.5.Pt16.5, ED
Bmmb
Bmmb
I41/a
1.650
1.636
-
-
1.983
γ- Al21Pt8
Al2Pt
χ
1.2964
1.2942(1)
0.5920
0.59194(9)
1.24
1.20953
2.354
2.34
Fm-3m
-
-
-
-
2.62
P31c
Pnma
-
2.6932
1.2339
1.24
ξ' = ε6
1.6556
1.65
14

Appendix 1.
Experimental diffraction data of the Al−Pt λ-phase indexed according to the structural model of Ref.
[5] (P3c1, a = 1.3089(2), c = 0.9633(1) nm). The intensities calculated from the model are added for
comparison. The alternative indexes for the same diffraction lines corresponding to a hypothetical
primitive cubic phase (a = 1.9257(7) nm) are added in the right column.
----------------------------------------------------
Rhomb.
Calc. Observed
Hypoth.cubic
No. h k l I/I0 I/I0
d
h k l
----------------------------------------------------
1
2
3
4
5
6
7
8
9
0 0 2
2 1 1
3 0 0
84 55
0.48164
0.39130
0.37794
0.29736
0.27057
0.24085
0.23958
0.22909
0.22591
0.22459
0.22014
0.21816
0.20921
0.20311
0.19871
0.18891
0.17590
0.16168
0.16055
0.14860
0.14775
0.14337
0.14282
0.13691
0.13217
0.13139
0.12930
0.12594
0.12283
0.12234
0.12186
0.12040
4 0 0
4 2 2
5 1 0
5 4 1
7 1 1
8 0 0
8 1 0
6 5 3
6 6 0
8 3 0
6 6 2
7 5 2
8 4 2
9 3 0
9 3 2
10 2 0
10 4 2
9 6 5
12 0 0
10 8 2
13 1 0
12 6 0
10 9 1
14 1 1
14 4 0
14 3 3
14 5 1
13 8 0
14 7 1
12 10 2
15 5 0
16 0 0
3
3
91 84
3 0 2 100 100
2 2 2
0 0 4
4 1 1
2 2 3
1 1 4
3 1 3
4 1 2
3 3 0
4 2 1
3 0 4
3 3 2
6 0 0
6 0 2
3 3 4
0 0 6
6 0 4
3 0 6
7 1 2
6 3 0
6 3 2
5 2 5
8 1 1
3 3 6
9 0 0
6 3 4
6 0 6
9 0 2
0 0 8
5
1
14 12
6
3
5
2
8
6
2
1
2
4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
49 34
4
3
62 55
68 46
16 12
23 19
22 13
3
3
13
9
15 11
1
2
8
6
23 16
1
2
10
1
1
5
4
7
16 10
12
12
3
9
6
1
----------------------------------------------------
15

Appendix 2.
Diffraction data of the Al−Pt ξ-phase (Bmmb, a = 1.9718(5), b = 1.6228(5), c = 1.4266(5) nm). From
the total of 112 collected reflections only those with I/I0 ≥ 10 % are given. The indexing is for the best
fit (aver. Δ(2θ) = 0.008 °, max. Δ(2θ) = 0.065 °, FOM(30) = 58.8).
----------------------------
h
k
l
d
I/I0
----------------------------
0
0
4
1
3
2
3
1
5
2
3
5
0
0
3
5
3
2
2
6
2
0
3
4
5
5
6
5
0
2
1
5
3
7
6
0
5
3
6
0
4
8
5
2
4
0
0
8
1
8
5
9
5
2
3
4
0
2
3
3
0
4
0
4
1
1
4
1
2
2
4
0
4
0
1
2
3
4
3
0
0
1
3
5
0
5
6
3
3
7
6
4
5
3
0
3
3
3
1
4
8
0
0
4
6
3
4
4
2
0
2
3
1
2
3
1
1
0
3
1
2
4
3
1
1
4
2
0
4
4
3
0
1
3
2
3
4
2
5
3
3
3
4
2
1
5
2
6
6
2
5
6
6
6
0
4
7
2
3
1
5
6
0.43086
0.40534
10
11
0.40086
23
0.39481
0.38524
0.38266
0.37984
0.37482
34
12
16
17
80
0.37001
0.35260
0.34806
56
57
41
0.34422
0.33537 100
30
0.33197
0.32858
73
14
0.32645
0.31370
12
24
0.31097
0.30361
0.29801
21
23
10
0.28296
0.22136
12
11
0.22037
0.21994
16
11
0.21770
0.21398
16
27
0.21258
40
0.20513
0.20278
49
76
0.20208
0.20082
69
66
-----------------------------
16

Appendix 2 (continue)
-----------------------------
h
k
l
d
I/I0
----------------------------
2
3
5
10
3
7
0
5
2
3
9
11
2
3
6
8
7
7
0
0
2
7
5
5
6
0
2
8
7
4
6
3
3
10
3
6
9
0
0
11
4
1
1
3
3
8
8
2
2
9
9
4
4
1
5
8
10
8
4
7
11
2
8
6
4
0
0
12
0
3
1
0
7
5
4
5
6
5
5
1
4
5
8
5
5
6
4
1
6
4
3
8
2
9
3
8
4
7
4
7
3
8
5
6
5
6
10
9
3
4
0
1
8
3
10
7
0
11
0
11
2
0.19858
38
0.19790
0.19718
0.19461
38
32
29
0.18829
0.17356
14
13
0.14614
5
9
11
10
2
13
8
6
13
8
0
3
13
8
12
9
0.14530
0.14449
2
5
0.14396
15
8
1
13
8
5
0.14338
0.14215
20
23
2
11
10
0
1
9
4
0.14139
0.14045
0.12324
14
13
10
10
13
0
1
0
3
12
1
16
5
6
-------------------------
17

a)
b)
c)
γ
Al2Pt
20μm
γ
λ
20μm
λ
100μm
Fig. 1 B. Grushko et al.

a)
b)
c)
20
30
40
50
60
2 θ, º
Fig. 2 B. Grushko et al.

a)
b)
1127
1128
Al
827
816
654
636
c)
d)
779
1028
1174
801
e)
Exo
817
600 700 800 900 1000 1100 1200
Temperature, ºC
Fig. 3 B. Grushko et al.

a)
b)
c)
0.1
0.2
0.3
1/d2, Å-2
0.4
0.5
Fig. 4 B. Grushko et al.

b)
a)
γ
γ
λ
50 μm
20 μm
d)
c)
λ
γ
ξ
ξ
γ
10 μm
10 μm
Fig. 5 B. Grushko et al.

a)
b)
c)
d)
20
30
40
50
60
2 θ, º
Fig. 6 B. Grushko et al.

a
b
c
Fig. 7 B. Grushko et al.

T, ºC
1400
1200
1000
800
1405
Al2Pt
L
1126
915
ξ
801
γ
817
(806)
655
(Al)
600
λ
400
30
20
10
Al
at.% Pt
Fig. 8 B. Grushko et al.

a)
c)
b)
530
813
998
u
1128
1125
a
d)
802
995
Exo
400
600
800
1000
1200
Temperature, ºC
Fig. 9 B. Grushko et al.

a)
b)
1087
774
783
945
1043
Al
Exo
Au
1000
400
600
800
Temperature, ºC
1200
Fig. 10 B. Grushko et al.




The constitution of Al−Pt above 65 at.% Al is specified.
The existence of the previously reported Al4Pt, A121Pt8 and A12Pt phases is conformed.
An additional stable orthorhombic phase was revealed at ~75-76 at.% Al and 801-915 °C.