Synthesis, extended and local crystal structure, and thermoelectric properties of Fe1-xRexGa3 solid solution

International audienceWe present a new Fe1–xRexGa3 solid solution, in which a 5d-metal––rhenium––partially substitutes for iron to the limiting composition of x = 0.10. The crystal structure refined for the composition Fe0.91Re0.09Ga3 shows the expected increase in the unit cell parameters compared to the parent FeGa3 compound, however the M–M (M = Fe, Re) distance decreases within the M–M dumbbell, indicating an increased M–M bonding density. Therein, investigation of the local structure by means of 69,71Ga NQR spectroscopy revealed the formation of homonuclear Fe–Fe and Re–Re dumbbells. Transport and thermoelectric properties have been investigated for the Re-substituted FeGa3. Electrical transport measurements showed preservation of the nonmetallic conductivity of Fe1–xRexGa3 despite the decrease of the valence electron concentration from 17 to 16.9 electrons per formula. At low temperatures, Fe1–xRexGa3 is a p-type semiconductor with the band gap of 0.4 eV, but with increasing temperature the sign of the dominant charge carriers changes. Owing to the alloying effect, Fe1–xRexGa3 displays 1.5 times lower thermal conductivity than FeGa3, which increases at high temperatures because of the growing contribution of the electronic term. © 201

New lead-free hybrid halometallates with dioctahedral anions synthesized using the template function of homopiperazine

Abstract New organic-inorganic hybrid halometallates of the general formula (HpipeH2)-[M2X10] · 2H2O, where M = Sb, Bi; X = Br, I; Hpipe is homopiperazine (C5N2H12), were synthesized. The crystal structures of three new compounds, α-(HpipeH2)2[Sb2I10] · 2H2O (1), β-(HpipeH2)2[Sb2I10)]-2H2O (2), and (HpipeH2)2[Bi2Br10] · 2H2O (3), were determined and analyzed in comparison with the previously synthesized analog (HpipeH2)2[Bi2I10] · 2H2O (4). All four compounds have similar crystal structures, in which inorganic dioctahedral [M2X10]4− anions alternate with organic (HpipeH2)2+ cations and water molecules to form 3D systems based on (N)H⋯X, (N)H⋯O, and (O)H⋯X hydrogen bonds. In all structures, the (HpipeH2)2+ cation serves the same template function, forming three (N)H⋯X hydrogen bonds with halogen atoms of the inorganic anion and one (N)H⋯O bond with a water molecule. In going from Sb to Bi and from I to Br, the band gap width increases and reaches 2.89 eV for compound 3

Synthesis, extended and local crystal structure, and thermoelectric properties of Fe1-xRexGa3 solid solution

We present a new Fe1–xRexGa3 solid solution, in which a 5d-metal––rhenium––partially substitutes for iron to the limiting composition of x = 0.10. The crystal structure refined for the composition Fe0.91Re0.09Ga3 shows the expected increase in the unit cell parameters compared to the parent FeGa3 compound, however the M–M (M = Fe, Re) distance decreases within the M–M dumbbell, indicating an increased M–M bonding density. Therein, investigation of the local structure by means of 69,71Ga NQR spectroscopy revealed the formation of homonuclear Fe–Fe and Re–Re dumbbells. Transport and thermoelectric properties have been investigated for the Re-substituted FeGa3. Electrical transport measurements showed preservation of the nonmetallic conductivity of Fe1–xRexGa3 despite the decrease of the valence electron concentration from 17 to 16.9 electrons per formula. At low temperatures, Fe1–xRexGa3 is a p-type semiconductor with the band gap of 0.4 eV, but with increasing temperature the sign of the dominant charge carriers changes. Owing to the alloying effect, Fe1–xRexGa3 displays 1.5 times lower thermal conductivity than FeGa3, which increases at high temperatures because of the growing contribution of the electronic term. © 201

Bulk and Surface Structure and High Temperature Thermoelectric Properties of Inverse Clathrate III in the Si P Te System

The creation of thermoelectric materials for waste heat recovery and direct solar energy conversion is a challenge that forces the development of compounds that combine appreciable thermoelectric figure-of-merit with high thermal and chemical stability. Here we propose a new candidate for high-temperature thermoelectric materials, the type-III Si172−xPxTey cationic clathrate, in which the framework is composed of partially ordered silicon and phosphorus atoms, whereas tellurium atoms occupy guest positions. We show that the utmost stability of this clathrate (up to 1500 K) in air is ensured by the formation of a nanosized layer of phosphorus-doped silica on the surface, which prevents further oxidation and degradation. As-cast (non-optimized) Si-P-Te clathrates display rather high values of the thermoelectric figure-of-merit (ZT=0.24–0.36) in the temperature range of 700–1100 K. These ZT values are comparable to the best values achieved for the properly doped transition-metal-oxide materials. The methods of the thermoelectric efficiency optimization are discussed

Crystal growth, electronic structure, and properties of Ni-substituted FeGa3

Crystals of the Fe1-xNixGa3 limited solid solution (xandlt;0.045) have been grown from gallium flux. We have explored the electronic structure as well as magnetic and thermoelectric properties of Fe0.975Ni0.025Ga3 in comparison with Fe0.95Co0.05Ga3, following the rigid band approach and assuming that one Ni atom donates twice the number of electrons as one Co atom. However, important differences between the Co- and Ni-doped compounds are found below 620 K, which is the temperature of the metal-to-insulator transition for both compounds. We have found that Fe0.975Ni0.025Ga3 displays lower degree of spatial inhomogeneity on the local level and exhibits diamagnetic behavior with a broad shallow minimum in the magnetic susceptibility near 35 K, in sharp contrast with the Curie-Weiss paramagnetism of Fe0.95Co0.05Ga3. Transport measurements have shown the maximum of the thermoelectric figure-of-merit ZT of 0.09 and 0.14 at 620 K for Fe0.975Ni0.025Ga3 and Fe0.95Co0.05Ga3, respectively. © 2015 Elsevier Inc. All rights reserved

Crystal growth, electronic structure, and properties of Ni-substituted FeGa3

International audienceCrystals of the Fe1-xNixGa3 limited solid solution (xandlt;0.045) have been grown from gallium flux. We have explored the electronic structure as well as magnetic and thermoelectric properties of Fe0.975Ni0.025Ga3 in comparison with Fe0.95Co0.05Ga3, following the rigid band approach and assuming that one Ni atom donates twice the number of electrons as one Co atom. However, important differences between the Co- and Ni-doped compounds are found below 620 K, which is the temperature of the metal-to-insulator transition for both compounds. We have found that Fe0.975Ni0.025Ga3 displays lower degree of spatial inhomogeneity on the local level and exhibits diamagnetic behavior with a broad shallow minimum in the magnetic susceptibility near 35 K, in sharp contrast with the Curie-Weiss paramagnetism of Fe0.95Co0.05Ga3. Transport measurements have shown the maximum of the thermoelectric figure-of-merit ZT of 0.09 and 0.14 at 620 K for Fe0.975Ni0.025Ga3 and Fe0.95Co0.05Ga3, respectively. © 2015 Elsevier Inc. All rights reserved

Crystal growth and electronic phase diagram of 4d doped Na1 delta Fe1 xRhxAs in comparison to 3d doped Na1 delta Fe1 xCoxAs

Single crystals of Na1 amp; 8722; amp; 948;Fe1 amp; 8722;xTxAs with T Co, Rh have been grown using a self flux technique. The crystals were thoroughly characterized by powder x ray diffraction, magnetic susceptibility, and electronic transport with particular focus on the Rh doped samples. Measurements of the specific heat and ARPES were conducted exemplarily for the optimally doped compositions. The spin density wave transition SDW observed for samples with low Rh concentration 0 amp; 8804;x amp; 8804;0.013 is fully suppressed in the optimally doped sample. The superconducting transition temperature Tc is enhanced from 10 K in Na1 amp; 8722; amp; 948;FeAs to 21 K in the optimally doped sample x 0.019 of the Na1 amp; 8722; amp; 948;Fe1 amp; 8722;xRhxAs series and decreases for the overdoped compounds, revealing a typical shape for the superconducting part of the electronic phase diagram. Remarkably, the phase diagram is almost identical to that of Co doped Na1 amp; 8722; amp; 948;FeAs, suggesting a generic phase diagram for both dopant