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A homologous series La n(n+1)+x Ni n(n+5)+y Si(n+1)(n+2)-z has beenobserved inthe La-Ni-Si representing a symmetric Ni-rich mirrorto the La(n+1)(n+2)Ni n(n-1)+2Si n(n+1). A series of fourhomologous silicides have been discovered duringsystematic explorations in the central part of the La-Ni-Sisystem at 1000 & DEG;C. All compounds La12.5Ni28.0Si18.3 (n = 3; a = 28.8686(8), c = 4.0737(2) & ANGS;, Z = 3), La22.1Ni39.0Si27.8 (n = 4; a = 20.9340(6), c = 4.1245(2) & ANGS;, Z = 1), La32.9Ni49.8Si39.3 (n = 5; a = 24.946(1), c = 4.1471(5) & ANGS;, Z = 1), and La44.8Ni66.1Si53.4 (n =6; a = 28.995(5), c = 4.158(1) & ANGS;, Z = 1) crystallize in the hexagonal space group P6(3)/m and can be generalizedaccording to La n(n+1)+x Ni n(n+5)+y Si(n+1)(n+2)-z with n = 3-6. Their crystalstructures are based on AlB2-type building blocks, fusedLa-centered Ni6Si6 hexagonal prisms, yieldinglarger oligomeric equilateral domains with the edge size equal to n. The domains extend along the c axisand show checkered ordering of the cationic and anionic parts, whileall their atoms are located on mirror planes. La n(n+1)+x Ni n(n+5)+y Si(n+1)(n+2)-z can beconsidered as a mirror series to the La-rich La(n+1)(n+2)Ni n(n-1)+2Si n(n+1), where an exchange of the formal cationic and anionic sites,i.e., La and Si, occurs. The La-Ni-Si system is thefirst system where two such analogous series have been observed.

The central part of the La-Ni-Si system has been investigated at 800 degrees C by means of single crystal X-ray diffraction, microscopy and analytical microprobe techniques. The result led to the identification of four new metal-rich silicides: LaNi2Si (R3m, a = 4.0263(3) angstrom, c = 15.066(2) angstrom, Z = 3), La2Ni3Si2 (P2(1)/c, a = 6.8789(7) angstrom, b = 6.2167(3) angstrom, c = 12.214(1) angstrom, beta = 90.92(1), Z = 4), La3Ni3Si2 (Pnma, a = 7.501(2) angstrom, b = 14.316(4) angstrom, c = 6.149(2) angstrom, Z = 4), La6Ni7Si4 (Pbcm, a = 6.066(1) angstrom, b = 7.488(1) angstrom, c = 29.682(5) angstrom, Z = 4). LaNi2Si belongs to the SrCu2Ga structure type, which is not represented among silicides, while La2Ni3Si2 crystallizes in its own structure type. Both compounds feature layered polyanionic motifs consisting of Ni and Si, which are separated by La. Instead, La6Ni7Si4 and La3Ni3Si2 are characterized by polyanionic networks. The former compound belongs to the Pr6Ni7Si4 structure type, with only two other representatives (Ce and Nd); the latter has been observed only with Rh and Ir. The two structures reveal close structural relationships having multiple identical slabs. Tight-binding electronic structure calculations by linear muffin-tin-orbital methods were performed for LaNi2Si, La2Ni3Si2 and La3Ni3Si2 to gain insights into their structure-bonding relationships. Their band structures suggest a metallic character for all compounds. The overall crystal orbital Hamilton populations are dominated by polar Ni-Si bonds, though homoatomic Ni-Ni and La-Ni(Si) bond contributions are not negligible. The variety of bonding patterns may serve as a logical explanation for the number of discovered compounds in this system as well as for the diversity of the observed structures.

Filled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Sm-y(FexNi1-x)(4)Sb-12-filled skutterudite system. Films were deposited under vacuum conditions by the pulsed laser deposition (PLD) method on fused silica substrates, and the deposition temperature was varied. The effect of the annealing process was studied by subjecting a set of films to a thermal treatment for 1 h at 423 K. Electrical conductivity sigma and Seebeck coefficient S were acquired by the four-probe method using a ZEM-3 apparatus performing cycles in the 348-523 K temperature range, recording both heating and cooling processes. Films deposited at room temperature required three cycles up to 523 K before being stabilized, thus revealing the importance of a proper annealing process in order to obtain reliable physical data. XRD analyses confirm the previous result, as only annealed films present a highly crystalline skutterudite not accompanied by extra phases. The power factor of annealed films is shown to be lower than in the corresponding bulk samples due to the lower Seebeck coefficients occurring in films. Room temperature thermal conductivity, on the contrary, shows values comparable to the ones of doubly doped bulk samples, thus highlighting the positive effect of interfaces on the introduction of scattering centers, and therefore on the reduction of thermal conductivity.

Filled skutterudites are currently studied as promising thermoelectric materials due to their high power factor and low thermal conductivity. The latter property, in particular, can be enhanced by adding scattering centers, such as the ones deriving from low dimensionality and the presence of interfaces. This work reports on the synthesis and characterization of thin films belonging to the Sm-y(FexNi1-x)(4)Sb-12-filled skutterudite system. Films were deposited under vacuum conditions by the pulsed laser deposition (PLD) method on fused silica substrates, and the deposition temperature was varied. The effect of the annealing process was studied by subjecting a set of films to a thermal treatment for 1 h at 423 K. Electrical conductivity sigma and Seebeck coefficient S were acquired by the four-probe method using a ZEM-3 apparatus performing cycles in the 348-523 K temperature range, recording both heating and cooling processes. Films deposited at room temperature required three cycles up to 523 K before being stabilized, thus revealing the importance of a proper annealing process in order to obtain reliable physical data. XRD analyses confirm the previous result, as only annealed films present a highly crystalline skutterudite not accompanied by extra phases. The power factor of annealed films is shown to be lower than in the corresponding bulk samples due to the lower Seebeck coefficients occurring in films. Room temperature thermal conductivity, on the contrary, shows values comparable to the ones of doubly doped bulk samples, thus highlighting the positive effect of interfaces on the introduction of scattering centers, and therefore on the reduction of thermal conductivity.

We investigated the U-Ni-B and Nb-Ni-B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U2Ni21B6 and Nb3-yNi20+yB6 [ternary derivatives of the cubic Cr23C6-type (cF116, Fm3m)] have been studied; the formation of the hypothetical U3Ni20B6 and Nb2Ni21B6 has been disproved. U2Ni21B6 [a = 10.6701(2) angstrom] crystallizes in the ordered W2Cr21C6-type, whereas Nb3-yNi20+yB6 [a = 10.5842(1) angstrom] adopts the Mg3Ni20B6-type. Ni in U2Ni21B6 can be substituted by U, leading to the solid solution U2-xNi21+yB6 (0 <= x <= 0.3); oppositely, Nb in Nb3Ni20B6 is partially replaced by Ni, forming the solution Nb3-yNi20+yB6 (0 <= y <= 0.5), none of them reaching the limit corresponding to the hypothetically ordered U3Ni20B6 and Nb2Ni21B6. These results prompted us to investigate quaternary compounds U2-zNbzNi21B6 and U6Nb3-delta Ni20B6: strong competition in the occupancy of the 4a and 8c sites by U, Nb, and Ni atoms has been observed, with the 4a site occupied by U/Ni atoms only and the 8c site filled by U/Nb atoms only. U2Ni21B6, U2.3Ni20.7B6, and Nb3Ni20B6 are Pauli paramagnets. Interestingly, Nb2.5Ni20.5B6 shows ferromagnetism with T-c approximate to 11 K; the Curie-Weiss fit gives an effective magnetic moment of 2.78 mu(B)/Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 mu(B)/fu (approximate to 0.49 mu(B)/Ni). The magnetic moment of Ni at the 4a site induces a moment in all of the Ni atoms of the whole unit cell (32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U2Ni21B6 and Nb3Ni20B6 is energetically preferred. The various electronic states generating ferromagnetism on Nb2.5Ni20.5B6 and Pauli paramagnetism on U2Ni21B6 and Nb3Ni20B6 have been

Twenty new ternary representatives of the Gd14Ag51 structure type have been synthesized within the R-Au-M family (R = Y, La-Nd, Sm-Tb, Ho, Er, Yb, Lu; M = Al, Ga, Ge, Sn, Sb, Bi) using solid state synthesis techniques. The list of post transition metals (M) involved in the formation of this type of structure could be augmented by five new representatives. All compounds crystallize in the hexagonal space group P6/m (#175) with the unit cell ranges of a = 12.3136(2)-12.918(1) angstrom and c = 8.9967(3)-9.385(1) angstrom, and incorporate different degrees of Au/M mixing. The involvement of the post transition element in the structure varies from one to another compound both qualitatively and quantitatively. A rather significant phase width can be expected for the majority of compounds, however, not without exclusions. The distribution of the post transition metals within the structure has been analyzed via single crystal X-ray diffraction. While the positional disorder of one near-origin Au position is expectable for all compounds due to steric reasons, two specimens show an obvious deviation from the others including another Au position split along the c axis. Possible factors affecting this behavior are discussed.