Novel ternary type-I clathrate compounds Ba(8){Zn,Cd}(x)Si(46-x), x∼7 have been synthesized from the elements by melting and reacting in quartz ampoules. Structural investigations for both compounds, i.e. x-ray single-crystal data at 300, 200 and 100 K for Ba(8)Zn(7)Si(39) and Rietveld data for Ba(8)Cd(7)Si(39), confirm cubic primitive symmetry consistent with the space group type [Formula: see text] (a(Ba(8)Zn(7)Si(39)) = 1.043 72(1) nm; a(Ba(8)Cd(7)Si(39)) = 1.058 66(3) nm). Whereas for Ba(8)Zn(7)Si(39) site 16i is completely occupied by Si atoms, a random atom distribution with different Zn/Si ratio exists for the two sites, 6d (0.77Zn+0.23Si) and 24k (0.91Si+0.09Zn). No vacancies are encountered and all atom sites are fully occupied. This atom distribution is independent of temperature. Rietveld refinements for Ba(8)Cd(7)Si(39) show that the 6d site is fully occupied by Cd atoms, leaving only the 24k site for a random occupation (0.96Si+0.04Cd) consistent with the chemical formula Ba(8)Cd(7)Si(39). The temperature-dependent x-ray spectra for Ba(8)Zn(7)Si(39) define an Einstein mode, Θ(E,U33) = 80 K. Studies of transport properties show electrons as the majority charge carriers in the system. Although the Cd- and Zn-based samples are isoelectronic, a significantly different electronic transport points towards substantial differences in the electronic density of states in both cases.

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In order to define the ability of magnetic elements M = Mn, Fe, Co to stabilise clathrate structures, alloys of the Ba – M – Ge system were investigated in the as-cast state and after annealing at 700°C and 800°C by means of X-ray powder diffraction, light optical and electron-probe microanalysis. Temperatures of phase transformations were derived from differential thermal analysis. Results are summarised in (i) isothermal sections at 700°C and 800°C, (ii) solidus and liquidus surfaces covering the region of existence for both clathrate phases in these systems. Invariant reactions during crystallisation are presented in form of Schultz – Scheil diagrams.In all three cases only limited solubility of the M element was found for clathrate IX (Ba6Ge25) i. e. the Ge-framework in the crystal structure of Ba6MxGe25 – x dissolves 0.6 atom of Mn, and about 1 atom of Fe and Co per unit cell. The maximum solubility of iron in clathrate type I (Ba8Ge46 – x) was found to be less than 0.5 Fe atom per unit cell, and clathrates with Mn and Co contain up to 1.0 and 2.5 atoms in the unit cell, respectively. Whilst Fe does not decrease the formation temperature of the clathrate phase, Mn and Co decrease it from 770°C (for binary Ba8Ge43) to 766°C and 749°C, respectively.