Compounds with Laves phases

Teslyk M.Yu. (1969) Metallic compounds with Laves phase s structure.-M. Nauka,1-196. 

Though the C16 or CuAh-type compounds are Laves phases and hence typical metals, their representatives TX2 with X being Sb, Ge, Sn or Pb, all show a trend towards formation of anion pairs (Fig. 31). In TiSb2 and VSb2 as well as e.g. in MnSna, FeGe2 or AuPba the anion-anion distance... 

There are several dozen metallic AB2 compounds called Laves phases that are superconducting they have either cubic or hexagonal crystal structures. Some have critical temperatures above 10 K and high upper critical magnetic fields Bc2- For example, Zri/2Hfi/2V2 has rc = 10.1K, B 2 = 24 T, and a compound with a different Zr/Hf ratio has similar and Bc2 values with the critical current density Jc 4 X 10 A/cm. These materials also have the advantage of not being as hard and brittle as some other intermetallics and alloys with comparable transition temperatures. 

Typically, binary Laves compounds AM2 are formed in several systems of A metals such as alkaline earths, rare earths, actinides, Ti, Zr, Hf, etc., with M = Al, Mg, VIII group metals, etc. Laves phases are formed also in several ternary systems either as solid solution fields extending from one binary phase (or possibly connecting the binary phases of two boundary systems) or as true ternary phases, that is forming homogeneity fields not connected with the boundary systems. 

Miedema s theory and structural information. The Miedema model for energy effects in alloys, presented in 2.2.1.3 has been very useful in an evaluation, albeit approximate, of the formation enthalpies and in the prediction of compound formation capability. For an example of the application and limits of this model, see the comments on the thermochemistry of the Laves phases reported in 3.9.3. However notice that the general usefulness of the Miedema approaches has diminished with time, both for its inherent approximation and for... 

Alloys with the 7th to 9th group elements. Several Laves phases are formed either as the hexagonal MgZn2 type (with Re, Fe, Ru, Os) or as the cubic Cu2Mg type (with Fe, Co, Rh, Ir). CsCl-type compounds are given mainly by Yb. 

Ru and Os alloys. A specimen of structure types observed in the alloys of these metals (very often as solid solution ranges) is shown in Table 5.48a. The formation of Laves-type phases, a phases and several CsCl-type phases can be underlined. Notice the formation of marcasite and pyrite type compounds with the semimetals and non-metals of the 15th and 16th groups. 

Among the actinide compounds the interest is concentrating on binary compounds of simple structure (e.g. 1 1 compounds with elements of the groups V and VI of the periodic table) for which the theoretical treatment is rather advanced, and on intermetal-lic (e.g. Laves-) phases. 

Comparison of the potassium content of the cetineite crystals to the composition of the synthesis mixture shows a preferred incorporation of potassium into the structure. Although this compound with 50 atoms per unit cell is a highly complex structure, it seems to follow the empirical Vegard s rule similar to homogeneous mixed crystals and for intermetallic phases of the Laves type as well as to microporous tin(IV)thioselenides of type SnSi.xSex.i.[13]... 

Abstract. The interaction of hydrogen with ZrMn2 Laves phase compound at pressure up to 60 atm and temperature range from 100 to 305 °C has been investigated using reaction calorimetry. The obtained results allow us to propose the existence of two hydride phase in the ZrMn2-H2 system. 

Luo, W., Clewley, J.D., Flanagan, T.B. and Oates, W.A. (1992) Thermodynamic Characterization of the Zr-Mn-H System Part 1. Reaction of H2 with Single-Phase ZrMn2+x C14 Laves Phase Alloys. J. Alloys. Compounds... 

Souberoux J.L., Fruchart D., Biris A.S. (1999) Structural studies of Laves phases ZrVCo(Vi xCrx) with 0[Pg.363]

Abstract. The interaction of hydrogen with nonstoichiometric Tio.9Zro.iMnL3Vo.5 Laves phase compound at pressure up to 60 atm and in temperature range from 150 to 190°C has been studied by means of calorimetric and P-X isotherm methods. The obtained results allow us to propose the existence of one hydride phase, 0-hydride, in the Ti0 9Zr0 jMnj 3V0 5 - H2 system in the temperature range 150-170°C. It has been found that temperature 190°C is close to critical temperature (182°C) above which hydride phases does not exist. 

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