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Journal of Alloys and Compounds 493 (2010) L33–L35

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

journa l homepage: www.e lsev ier .com/ locate / ja l l com

etter

bservation of the new binary low temperatures compound AlV

eatrix Huber, Klaus W. Richter ∗

niversity of Vienna, Department of Inorganic Chemistry/Materials Chemistry, Währingerstraße 42, 1090 Wien, Austria

r t i c l e i n f o

rticle history:eceived 23 November 2009eceived in revised form3 December 2009

a b s t r a c t

Up to now, the binary Al–V system was only investigated at temperatures of 600 ◦C and above. In thecourse of a re-investigation of the system at 500 ◦C, the new compound AlV was discovered. Annealingexperiments point to a decomposition temperature around 540 ◦C, but the respective thermal effect could

ccepted 24 December 2009vailable online 4 January 2010

eywords:–V phase diagramrystal structure

not be detected in DTA experiments due to the sluggish and slow reaction. The composition of the phasewas determined to be Al50.1(5)V46.9(5) by means of EPMA. In order to determine the crystal structure ofthe new phase, several attempts were done to prepare single crystals for single crystal XRD. Due to thepoor crystallization of the phase, it was not possible to gain suitable crystals for structure determination.Indexing of the powder pattern indicates the phase to be of tetragonal symmetry (possible space groupP42212) with the cell parameters a = 10.845(1) Å and c = 4.3755(2) Å. The cell determination was only

cryst

emperature phase tentative due to the poor

. Introduction and literature review

The binary Al–V system has been investigated repeatedly and,mong others, it is given in Massalski’s Handbook of Binary Alloyhase Diagrams [1]. A detailed review of the system was given byurray [2]. In the binary Al–V system five different phases have

een found to exist: Al21V2 (cF184, Fd-3m, Al21V2-type), Al45V7mC104, C2/m, Al45V7-type), Al23V4 (hP54, P63/mmc, Al23V4-type),l3V (tI8, I4/mmm, Al3Ti-type) and Al8V5 (cI52, I-43m, Cu5Zn8-

ype). On the basis of microstructure observation, XRD and thermalnalysis Carlson et al. [3] determined the phase diagram for thehole composition range. They investigated the system at tem-eratures of 600 ◦C and above. Considering the change of the cellarameter of bcc-(V) they determined the phase boundary of theolid solution of Al in V. They found 42.0 at.% Al at 600 ◦C, 43.5 at.%l at 800 ◦C, 45.0 at.% Al at 900 ◦C and 64.0 at.% Al at 1000 ◦C,espectively. Furthermore they suggested a noticeable homogene-ty range for the phase Al8V5 although precise data are missingn this respect. The phase equilibria in the Al-rich part of the Al–Vystem are quite complex and were later re-investigated by Richternd Ipser [4]. They investigated the system at 630 and 1050 ◦C andeasured significant differences concerning the invariant reaction

emperatures. All five compounds were found to melt peritectically.

nly two of the phases, Al3V and Al8V5, show a small homogene-

ty range. According to their measurements the solid solution ofl in V reaches 48.5 at.% Al at 1050 ◦C. Recently, Gong et al. [5]erformed a thermodynamic reassessment of the system includ-

∗ Corresponding author.E-mail address: klaus.richter@univie.ac.at (K.W. Richter).

925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.jallcom.2009.12.142

allinity of the compound.© 2010 Elsevier B.V. All rights reserved.

ing the results of [3] and [4] to their optimization. According totheir calculations, in comparison to Richter and Ipser the Al con-tent in (V) increases slightly to 46.5 at.% Al at 1050 ◦C and 39.0 at.%Al at 500 ◦C, respectively. The maximum solubility of Al in bcc-(v)is reached at the temperature of the peritectic decomposition ofAl8V5 and was found to be between ∼54 at.% [3] and ∼50 at.% [4]Al.

In the course of an ongoing research with the aim to clarifythe phase equilibria in the ternary Al–Si–V system [8], we also re-investigated the temperature-dependent solubility of Al in V. In thecourse of this study we discovered a new binary AlV compound atlower temperatures.

2. Experimental

The samples were prepared from aluminum slug (99.999%, Alfa Aesar, Karl-sruhe, Germany) and vanadium pieces (99.7%). To remove oxides at the vanadiumsurface it was treated with diluted hydrochloric acid for some minutes in the ultra-sonic bath. After rinsing it with water and acetone it was dried for some minutes at120 ◦C. Calculated amounts of the elements were weighed to an accuracy of 0.05 mgand arc melted on a water-cooled copper plate under an argon atmosphere. Zir-conium was used as a getter material within the arc chamber. The reguli with atotal mass of about 1000 mg were remelted three times for good homogenizationand weighted back after each melting step to control the mass losses. The totalmass losses were less than 1% and can be considered to be negligible. The reg-uli were placed into alumina crucibles, which were sealed into evacuated quartzglass ampoules and heat treated for 3 weeks at 500 and 620 ◦C, respectively. Afterquenching in cold water the samples were separated into several pieces, which were

investigated by optical microscopy (Zeiss Axiotech 100), EPMA (Jeol JXA 733 Super-probe, 15 kV, 20 nA, conventional ZAF matrix correction was use to calculate thefinal composition from the measured X-ray intensities) and powder XRD (BrukerD8 Advance Diffractometer operating in reflection mode, Cu K� radiation, Lynxeyesilicon strip detector). All powder patterns were analyzed using the TOPAS software[6].

L34 B. Huber, K.W. Richter / Journal of Alloys and Compounds 493 (2010) L33–L35

nnealed at 620 ◦C (dashed line) and 500 ◦C (solid line), respectively.

3

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F5

Fig. 1. Comparison of the X-ray powder patterns of samples a

. Results and discussion

Samples with the nominal composition Al50V50, annealed at20 and 500 ◦C, respectively, showed significantly different X-rayowder patterns (Fig. 1). While the pattern observed for 620 ◦Cas identified as a mixture of Al8V5 and the solid solution of Al

n bcc-(v), the sample annealed at 500 ◦C showed a completelyifferent pattern which could not be identified with any knownrystal structure in the Al–V system. However, the pattern showedtrong peaks near to the peaks of bcc-(V) pointing to some rela-ions to this simple structure. In Fig. 2 a BSE image of the sampleith the nominal composition Al50V50 annealed at 500 ◦C is shown.

he composition of the new binary compound was determinedy means of EPMA and corresponds to the chemical compositionl50.1(5)V49.9(4). Beside the main phase AlV, small amounts of thearker phase Al8V5 can be seen. For this phase the composition waseasured to be 60.2(5) at.% aluminium and 49.8(5) at.% vanadium

y means of EPMA. The sample containing the new AlV-phase wasnvestigated by DTA in order to determine the transition tempera-ure, but no noticeable effect was found in the temperature rangeetween 500 and 620 ◦C. In order to determine the exact decom-osition temperature, different annealing temperatures (590, 560,

◦

45, 540, 535 and 530 C) were applied; the annealing time was 4eeks. At 535 ◦C we observed the best pattern; i.e. the (V) maineak (0 1 1) at around 41.5◦ (2�) was not visible as dominant peak.tarting from 540 ◦C, the (V) (0 1 1) peak started to grow and at90 ◦C the pattern was completely converted to simple bcc. Thus

ig. 2. BSE image of a sample with the nominal composition Al50V50 annealed at00 ◦C.

Fig. 3. Temperature program for the oscillation annealing used for the improvementof crystal quality.

we concluded that the formation temperature of the new phaseis below 540 ◦C. The crystals isolated from the sample annealedat 535 ◦C were of low quality and could not be used for structuredetermination. In order to gain single crystals for structure deter-mination (NONIUS four circle diffractometer, CCD detector, 300 �mcapillary optics collimator, Mo tube, graphite monochromator) sev-eral attempts were made to improve the crystal quality and size.A sample which was annealed at 535 ◦C was oscillated around thehypothetic decomposing temperature of 540 ◦C several times. Therespective temperature program can be seen in Fig. 3. A similar pro-cedure was successfully used to grow suitable single crystals in apure solid–solid reaction in the Al–Ni–Si system [7]. In the currentcase, however, subsequent single crystals measurements indicatedthat the sample was crystallized insufficiently and showed mosaiclike crystallization. Therefore structure determination was impos-sible.

In another attempt we tried to use iodine as crystallization aid.For this purpose the coarsely powdered sample and about 10 mg ofI2 were put into a quartz glass tube which subsequently was evac-uated and sealed. For annealing in the muffle furnace two differentprocedures were applied. On the one hand isothermal annealing at535 ◦C for 6 weeks was performed. These samples again exhibitedmosaic like crystallization of the new phase, not suitable for singlecrystal XRD. The other annealing experiments were done using atemperature program which can be seen in Table 1. The temper-

ature was risen over the decomposition temperature up to 560 ◦Cwith the aim to gain better crystallization on slow cooling. Fig. 4shows a comparison of the XRD patterns of a sample annealed reg-ularly at 535 ◦C and a sample annealed with I2 as crystallization aid

Table 1Temperature program with I2 as crystallization aid.

Segment Temperature Cooling-/heating rate Duration

Heating 560 ◦C 1 K/minCooling 535 ◦C 1 K/minIsothermal 100 hHeating 560 ◦C 1 K/minCooling 535 ◦C 1 K/minIsothermal 100 h

B. Huber, K.W. Richter / Journal of Alloys and Compounds 493 (2010) L33–L35 L35

Fig. 4. Comparison of the X-ray powder patterns of samples after annealing at 535 ◦C (between 560 and 535 ◦C using I2 as crystallization aid (dashed line), respectively.

Table 2Result of the indexing of the powder pattern of a sample annealed at 535 ◦C.

Obs. position/2� Area h k l Theor. position/2�

18.31 2.65 2 1 0 18.2827.41 4.28 2 1 1 27.4332.99 2.96 3 1 1 33.1636.60 4.97 3 2 1 36.2137.03 3.41 4 2 0 37.0439.33 35.81 0 4 1 39.0540.09 13.06 4 1 1 39.9641.15 68.16 0 0 2 41.2341.59 102.10 4 3 0 41.6042.13 82.93 0 1 2 42.10

42.57 78.47 5 1 0 42.474 2 1 42.59

44.61 23.37 0 2 2 44.63

56.80 9.77 4 2 2 56.626 3 0 56.91

58.22 39.63 5 4 1 58.3860.23 22.62 5 5 0 60.3064.60 22.69 4 4 2 64.5870.07 10.78 3 1 3 70.05

73.92 16.13 0 4 3 73.706 6 0 74.13

75.35 25.51 7 5 0 75.328 2 1 75.41

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75.74 80.89 7 1 2 75.6776.06 50.93 4 2 3 76.0977.49 23.04 7 2 2 77.4579.41 32.32 5 1 3 79.64

ith temperature program. As can be seen, also the use of I2 wasot successful to form high quality crystals and cycling between60 and 535 ◦C even yielded in the complete decomposition of theew phase into (V) and Al8V5. In the light of these observations itannot be ruled out, that AlV shows a true decomposition temper-ture even lower than 535 ◦C or that it is in fact a metastable phase.iven the slow kinetics at this rather low temperature, long-term

nnealing experiments at different temperatures, with and withoutrystallization aid are necessary to come to a final conclusion.

As we were not able to prepare good single crystals, we tried toetermine the unit cell of the phase from powder data. Indexing ofhe powder pattern of the sample annealed at 535 ◦C was performed

[

[[[

solid line, X-ray measurement was done with monochromator) and after cycling

using the TOPAS software [6]. Due to the rather low crystallinity ofthe compound (the domain size refined with a fundamental param-eter approach was 26 nm), the diffraction peaks were rather broad,and the distinction of partly overlapping peaks was not alwaysunambiguous. The most suitable result indicates the phase to beof tetragonal symmetry, possible space group P42212 with thecell parameters a = 10.8450(7) Å and c = 4.3755(2) Å, respectively.The cell parameter for bcc-(V) at the same composition at highertemperatures was determined to be a = 3.0692(1) Å. This value isassociated to the cell parameters of the suggested tetragonal cellby the factor

√2 for c and by the factor (5/2)

√2, for a, respectively.

This indicates a possible superstructure relation to the simple bccstructure. In Table 2 the positions and intensities of the observedpeaks are listed together with the Miller indices and the theoreti-cal positions of the diffraction lines of the tetragonal cell. With fewexceptions, the peaks match very well with the theoretical position.For four peaks two different h k l are listed because of ambiguity.Although the cell proposed here is quite reasonable given the cellparameter relations to bcc-(V), the solution should still be takenwith some caution, as the crystalline quality of the investigatedsamples was not sufficient for unambiguous indexing.

Single crystal measurements will be essential for structuredetermination and further attempts with regard to gain suitablesingle crystals are in progress.

Acknowledgements

Financial support from the Austrian Science Foundation (FWF)under the project number P19305 is gratefully acknowledged. Theauthors wish to thank Sasha Kodentsov from the Eindhoven Uni-versity of Technology for experimental support.

References

1] T.B. Massalski, H. Okamoto, P.R. Subramanian, L. Kacprzak, Binary Alloy PhaseDiagrams 1–3 (1990).

2] J.L. Murray, Bull. Alloy Phase Diagrams 10 (1989) 351.3] O.N. Carlson, D.J. Kenny, H.A. Wilhelm, Trans. Am. Soc. Met. 1 (1954) 20.4] K.W. Richter, H. Ipser, Z. Metallkde 91 (2000) 383.

5] W.P. Gong, Y. Du, B.Y. Huang, R. Schmid-Fetzer, C.F. Zhang, H.H. Xu, Z. Metallkde

95 (2004) 978.6] Topas, Version 3.0, Brucker AXS Inc., Karlsruhe, Germany, 1999.7] K.W. Richter, Y. Prots, Y. Grin, Z. Anorg. Allg. Chem. 630 (2004) 417.8] B. Huber, H.S. Effenberger, K.W. Richter, Intermetallics, 2009, doi:10.1016/

j.intermet.2009.10.016.