Composition dependence of the glass transition temperatures of PdNiP and PtNiP glasses

Journal of Non-Crystalline Solids 12 ( 1973) 333- 338. © North-Holland Publishing Company

COMPOSITION DEPENDENCE OF TIlE GLASS TRANSITION TEMPERATURES OF Pd-Ni-P AND Pt-Ni-P GLASSES H.S. CHEN Bell Laboratories, Murray Hill, New Jersey 07974, USA

Received 16 March 1973

Thermal properties of glassy Pd-Ni-P and Pt-Ni-P alloys have been measured as a function of the concentration of transition metals. The glass transition temperature, Tg, of these alloy glasses exhibits a negative linear deviation with transition metal content - which is in contrast to the increasing Tg of binary glassy alloys with increasing metalloids. It is suggested that the suppression of the glass transition temperature of these glassy alloys may be attributed to the excess configurational entropy of disorder associated with a mixture of hard spheres differing in radius. In contrast, the increasing Tg of binary glassy alloys with the metalloid content may be associated with the short-range order resulting from strong interactions between metal and metalloid atoms.

1. Introduction Alloys of P d - N i - P and P t - N i - P can be melt-quenched into amorphous solids for a wide composition range of transition metals. The structure and electrical properties of these amorphous alloys have been studied extensively [1, 2]. X-ray studies revealed that the mean interatomic distance r 1 of the amorphous alloys, reduced from the radial distribution function, varied linearly with the concentration of the transition metals. It was therefore suggested that Ni atoms could replace Pd or Pt atoms substitutionally without drastic changes in the structure. We report here some thermal properties of the glassy alloys as a function o f : transition metal content. The composition dependence of the glass transition ~temperature of these glassy alloys is discussed in terms of thermodynamic properties of disorder associated with the hard-sphere assembly.

2. Experimental Binary alloys o f Pd0.80P0.20, Pt0.75P0.25, Ni0.80P0.20 and Ni0.75P0.25 were prepared by proper mixing of the element powders and then sintering the mixture prior to melting. Detailed procedures have been described elsewhere [3]. The starting

334

H.S. Chen, P d - N i - P and P t - N i - P glasses

Table 1 Thermal properties of glassy (Pdl_xNix)o.80Po.20, (Ptl_yNiy)o.Ts Po.2s , and (1 - z)Pto.TsPo.2s + z Nio.80Po.20 alloys. Composition

Tg

Tc

ACp

AHc

x-- 0.80 0.70 0.59 0.46 0.34 0.21 0.10

588 585 585 587 590 596 604

627 642 634 636 634 630 611

5.45-5.85 5.55 5.53-6.00 6.35 4.90-5.50 5.40-6.30 5.45

850 945 965 1180 1090 900 930

y= 0.80 0.60 0.40 0.30

485 502 542 570

537 542 555 575

7.37-7.90 7.13 5.70 4.40

1560 1655 1560 1130

z= 0.80 0.60 0.40 0.30 0.20

484 503 538 552 (~570)

524 532 552 555 610

7.55-8.10 6.83 5.40-5.80 4.70-5.10 -

1440 1450 1500 1240 1150

Tg is the glass transition temperature in deg K, ACp is the specific heat increment at Tg in cal/ mole • deg K, Tc in deg K and AHc in cal/mole are respectively the onset temperature and the heat of crystallization.

materials were palladium and platinum powders of 99.99% purity, nickel powders of 99.9% purity, and reagent-grade red phosphorus powders. Three series o f ternary alloys (Pd 1-x Nix)0.80Po.20; (Pt 1-y Niy)0.75 P0.25 and (1 - z )Pt 0.75 P0.25 + (z)Nio.80Po.20 were obtained by realloying the required amounts o f the binary alloys. Alloying processes were usually carried out in a capsulated fused quartz tube that prevented the preferential vaporization o f phosphides. Glassy alloys were obtained by the roller quenching technique [4]. About 1 g of alloy melt was ejected from an orifice of about 150 #m in diameter. The structure of the quenched foils was examined with an X-ray diffractometer using either CuKa or MoK~ radiation. Alloys with composition 0.20 <_x <_ 0.90, 0.20 <_y <_ 0.70, and 0.20 <_ z <_ 0.80 could be quenched into a glassy state with a high degree of reproducibility. The stability of the glassy alloys was examined with a differential scanning calorimeter using a scanning rate of 20°C/min. Glassy alloys in general crystallized in several steps above Tg when they were heated to 500°C.

H.S. Chen, P d - N i - P and P t - N i - P glasses

335

660

/t

640

620

600

580

i/ Ij

/

560

i

540

520

500

480 I

I 0.2

,

I a4

I

I a6

I

I ~8

, 1.0

COMPOSITIONS X.Y,Z Fig. 1. The composition dependence of the glass transition temperature Tg of glassy alloys. *: (pdl_xNix)o.soPo.20; o: (ptl_yNiy)o,TsPo.2s , and ~: (1 - x)Pto.TsPo.2s + z Nio.80Po.20 alloys.

3. Results The thermal properties of the glassy alloys near the glass transition temperature Tg are listed in table 1, where ACp is the specific heat increment at Tg, and Tc and AHc are respectively the onset temperature and the heat of crystallization, and the composition dependence of Tg is illustrated in fig. 1. It is noted that the glass transition temperature of both glassy P d - N i - P and P t - N i - P alloys showed a negative linear deviation with the concentration of transition metal. The maximum deviation is about 22 and 45 K respectively for (Pdl_xNix)o.80P0.20 and (Ptl_yNiy)0.75P0.25 glassy alloys near the equiatomic concentration of the transition metals. The addition of P into P t - N i - P alloys in contrast, greatly increased the Tg of the glassy alloys. Extrapolation of Tg versus composition yields Tg -~ 600, 470,615 and 660 K for glassy Pd0.80Po.20, Pto.75P0.25, Ni0.80P0.20 and Ni0.75Po.25 alloys respectively.

336

H.S. Chen, P d - N i - P and P t - N i - P glasses

These glassy alloys are relatively stable. The temperature difference between the crystallization temperature Tc and the glass transition temperature Tg, AT, attained as high as 57°C for (Pd0.70Ni0.30)0.80P0.20 and 52°C for (Pt0.80Ni0.20)0.75 P0.25 alloys. It is noted that the most stable glasses lie near either Pd or Pt rich boundaries of the glass forming regions. The inconsistency between the ease of glass formation and the stability of glassy alloys has also been observed for Pd-Si [5] and Au---Ge-Si alloys [6]. It is therefore suggested that the factors which control the formation and the subsequent stability of glassy alloys involve different crystallization processes. This point will be elaborated further in a separate paper. The increment in the specific heat at Tg(ACp) was about 5.50 cal/mole • °C for glassy P d - N i - P alloys. ACp of the glassy P t - N i - P alloys however increased from 5.00 to 8.00 cal/mole • °C with increasing Pt content. A strong composition dependence of the heat of crystallization AH e was also observed for P t - N i - P alloys. AHc varies from 1000 to 1600 cal/mole.

4. Discussion The admixture of transition metals suppressed the glass transition temperature Tg of glassy P d - N i - P and P t - N i - P alloys which contrasts to the observation that Tg of glassy Pd-Si [5, 7], Au-Si [8] and Ni-P alloys increases with increasing metalloid content. As the relative atomic volume of Ni to Pd, and Ni to Pt are similar to those of metalloid atoms to corresponding metal atoms, with exception of Ni-P alloys, the apparent discrepancy in the composition dependence of Tg on metals and metalloids cannot be described by the difference in the atomic volume of the constituents alone. It has been pointed out [5] that the chemical bonding between constituent atoms plays an important role in structure and properties of glassy metals. Many metallic binary liquid alloys, such as Pb-Sn, Sb-Cd [9], F e - C [10] and Fe-Si [11], as well as organic liquid mixtures [12] above the melting point exhibit a negative deviation of viscosity though the excess volume of the alloys may be negative. It is observed that the larger the difference in the atomic size, the stronger will be the negative deviation of the mixture. If this trend persists down to the glass transition temperature, one would expect a negative deviation of glass transition temperature with composition as it is observed for the glassy P d - N i - P and P t - N i - P alloys. The causes of this behavior are not clear. It is probable that the random mixing of atoms of different sizes enhances the configurational entropy of the system~ This point will be elaborated as follows. It has been suggested [13-15] that the structure and entropy of disorder associated with the hard-sphere assembly can be applicable to liquid alloys. Computer calculations of the thermodynamic properties of hard-sphere mixtures showed that [l 6, 17] under a constant pressure a mixture of hard spheres differing in radius exhibits a positive excess entropy, but a negative excess volume over an assembly of uniform hard spheres.

H.S. Chen, Pd-Ni-P and Pt-Ni-P glasses

337

Since the interactions between either Ni and Pd or Ni and Pt [18] are not very strong, we may assume that Ni atoms can be substituted for Pd or Pt atoms randomly without a drastic change in structure. The excess configurational entropy of the alloy mixtures therefore may be associated with the excess entropy of a random hard-sphere mixture. Since the atomic volume of Ni is about 35% less than that of Pd or Pt, admixture of these transition metals would yield a positive excess configurational entropy and therefore a negative excess viscosity. It is suggested therefore that the suppression of the glass transition temperature of glassy P d - N i - P and P t - N i - P alloys may be attributed to the excess entropy of a random mixture of hard spheres differing in radius. We neglect here the effects of existing phosphorus on the entropy of the alloy mixture. The increasing Tg of binary alloy glasses with metalloid content, in contrast, may be attributed to the strong bonding between metals and metalloids. Quasi-chemical approximation [19] shows that the entropy associated with compositional ordering AS ° may approximate to x2(1 - x ) 2 X 2 / z R T 2, where X is the interatomic binding energy constant, x is the molar fraction of metalloid, z is the coordination number. Above melting temperatures, the ordering effect in general is small and the viscosity or alloys usually decreases on alloying due to a difference in atomic volume of the constituents. With falling temperature, AS ° decreases and finally at a certain temperature, IAS°I approaches the theoretical compositional entropy -~,ixi In x i. The liquid mixture then attains a very high degree of compositional and therefore structural order. For the binary glassy alloys mentioned above, x ~ 0.2, X/RTg -~ - 1 5 , and z ~ 12, it yields IAS°I ~ 0.48R which is of the order of the total compositional entropy. This indicates that the binary glassy alloys attain a higher degree of order near the glass transition temperature. It has been observed that either ordering or clustering of liquid mixtures [ 12, 20] enhances the viscosity. Thus, the increasing Tg of the binary alloy glasses with metalloid contents may be attributed to the increasing viscosity associated with the increasing ordering of liquid alloys near the glass transition temperature.

Acknowledgements The author is in debt to Professor P. Duwez for supplying the initial specimens of glassy P d - N i - P alloys, and Dr. J.D. Weeks for pointing out the computer calculations of hard spheres mixtures.

References [1] P.L. Maitrepierre, J. Appl. Phys. 40 (1969) 4826; 41 (1970) 498. [2] A.K. Sinha and P. Duwez, J. Phys. Chem. Solids, 32 (1971) 267; A.K. Sinha, Phys. Rev. AI (1970) 12.

338 [3] [4] [5] [6] [7] [8] [9] [10] [ 11 ] [121 [13] [14] [15] [16] [17]

H.S. Chen, P d - N i - P and P t - N i - P glasses

S.C.H. Lin and P. Duwez, Phys. Stat. Sol. 34 (1969) 669. H.S. Chen and C.E. Miller, Rev. Sci. Inst. 41 (1970) 1237. H.S. Chert and B.K. Park, Acta Met., 21 (1973) 395. H.S. Chen and D. Turnbull, Acta Met. 18 (1970) 261. H.S. (?hen and D. Turnbull, Acta Met. 17 (1969) 1021. H.S. Chen and D. Turnbull, J. Chem. Phys. 48 (1968) 2560. H.J. Fisher and A. Phillips, J. Metals, Trans. AIME 6 (1954) 1060. R.N. Barfield and J.A. Kitchener, J. Iron and Steel Inst. 180 (1955) 324. A.A. Romanov and V.G. Kochegarov, Fiz. Metal. Metalloid, 17 (1964) 1112. R.J. Fort and W.R. Moore, Tran. Faraday Soc. 62 (1966) 1112. H.C. Anderson, J.D. Weeks and D. Chandler, Phys. Rev. A 4 (1971) 1597. L.G. Caron, J. Chem. Phys. 55 (1971) 5227. C.H. Bennet, D.E. Polk and D. Turnbull, Acta Met. 19 (1971) 1295. B.J. Alder, J. Chem. Phys. 40 (1964) 2724. G.A. Mansoori, N.F. Carnahan, K.E. Starling and T.W. Leland, Jr., J. Chem. Phys. 54 (1971) 1523. [18] K. Schwerdtfeger and A. Muan, Acta Met. 13 (1965) 509. [19] O.J. Kleppa, Liquid Metals and Solidification, The 39th National Metal Congress and Exposition, ASM (1958). [20] J. Brunet and K.E. Gubhins, Tran. Faraday Soc. 65 (1969) 1255.