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The presence of one-dimensional trigonal arrangements of chromium atoms (Cr-3) in the structure of TiCrIr2B2 leads to a magnetic transition near ambient temperature. Herein we report an investigation of the nature of electronic and magnetic properties of TiCrIr2B2 via ab initio calculations together with B-11 NMR Knight shift (K) and spin-lattice relaxation rate (1/T1) analysis. The presence of a characteristic rectangular powder pattern below 280 K, absence of a Korringa relation, strong enhancement of 1/TI.T at low temperatures and weak temperature dependence of K indicate competition between antiferromagnetic and ferromagnetic spin fluctuations in the itinerant d-band electrons, in agreement with ab initio calculations. One-dimensional trigonal arrangements of magnetically active elements in intermetallic compounds, as is found in TiCrIr2B2, are quite rare and could lead to exotic phenomena such as spin-chirality and quantum criticality in low-dimensional frustrated lattices.

Non-oxide perovskites exhibit unusual properties such as negative thermal expansion, negative thermal coefficient of resistance, positive and negative giant magnetoresistance as well as superconductivity. These uncommon properties appear to originate from the basic structure only, in strong contrast to the oxides. Ordering in nonstoichiometric compounds may not only lead to different chemical compositions but also to the promotion of these physical properties. We present a combined NMR and first-principles study of the cubic Zr 2 Ir 6 B perovskite to investigate the boron ordering with boron deficiency leading to the formation of superstructure. Competing ionic and metallic interactions reflect the semimetallic character of this boride and result in the formation of a pseudogap, as predicted by our first principles calculations and verified experimentally by 11 B solid state NMR. Several avoided crossing scenarios were also found for the bands from the conducting states at +1 eV to the Fermi level along specific directions. This observation is of paramount importance for understanding the structure-property relationships in metal boride perovskites and the search for new cubic perovskites.

SrPt3Al2, a CaCu5 relative (P6/mmm; a = 566.29(3), c = 389.39(3) pm; wR2 = 0.0202, 121 F2 values, 9 parameters), and Sr2Pd2Al, isostructural to Ca2Pt2Ge (Fdd2; a = 1041.45(5), b = 1558.24(7), c = 604.37(3) pm; wR2 = 0.0291, 844 F2 values, 25 parameters) have been prepared from the elements. The crystal structures have been investigated by single crystal X-ray diffraction. Structural relaxation confirmed the electronic stability of SrPt3Al2, while orthorhombic Sr2Pd2Al might be a metastable polymorph as it is energetically competitive to its monoclinic variant. Both compounds are predicted to be metallic conductors as their density-of-states (DOS) are non-zero at the Fermi level. COHP bonding analysis coupled with Bader effective charge analysis suggest that the title compounds are polar intermetallic phases in which strong Pt–Al and Pd–Al covalent bonds are present, while a significant electron transfer from Sr atoms to the [Pt3Al2]δ– or [Pd2Al]δ– network is found.

The new ternary transition metal-rich borides Ta2OsB2 and TaRuB have been successfully synthesized by arc-melting the elements in a water-cooled crucible under an argon atmosphere. The crystal structures of both compounds were solved by single-crystal X-ray diffraction and their metal compositions were confirmed by EDX analysis. It was found that Ta2OsB2 and TaRuB crystallize in the tetragonal Nb2OsB2 (space group P4/mnc, no. 128) and the orthorhombic NbRuB (space group Pmma, no. 51) structure types with lattice parameters a=5.878(2) A, c=6.857(2) A and a=10.806(2) A, b=3.196(1) A, c=6.312(2) A, respectively. Furthermore, crystallographic, electronic and bonding characteristics have been studied by density functional theory (DFT). Electronic structure relaxation has confirmed the crystallographic parameters while COHP bonding analysis indicates that B2-dummbells are the strongest bonds in both compounds. Moreover, the formation of osmium dumbbells in Ta2OsB2 through a Peierls distortion along the c-axis, is found to be the origin of superstructure formation. Magnetic susceptibility measurements reveal that the two phases are Pauli paramagnets, thus confirming the theoretical DOS prediction of metallic character. Also hints of superconductivity are found in the two phases, however lack of single phase samples has prevented confirmation. Furthermore, the thermodynamic stability of the two modifications of AMB (A=Nb, Ta; M =Ru, Os) are studied using DFT, as new possible phases containing either B4- or B2-units are predicted, the former being the most thermodynamically stable modification.

The intermetallic compound EuAu3Al2 has been prepared by reaction of the elements in tantalum ampules. The structure was refined from single-crystal data, indicating that the title compound crystallizes in the orthorhombic crystal system (a = 1310.36(4), b = 547.87(1), c = 681.26(2) pm) with space group Pnma (wR2 = 0.0266, 1038 F(2) values, 35 parameters) and is isostructural to SrAu3Al2 (LT-SrZn5 type). Full ordering of the gold and aluminum atoms was observed. Theoretical calculations confirm that the title compound can be described as a polar intermetallic phase containing a polyanionic [Au3Al2](δ-) network featuring interconnected strands of edge-sharing [AlAu4] tetrahedra. Magnetic measurements and (151)Eu Mössbauer spectroscopic investigations confirmed the divalent character of the europium atoms. Ferromagnetic ordering below TC = 16.5(1) K was observed. Heat capacity measurements showed a λ-type anomaly at T = 15.7(1) K, in line with the ordering temperature from the susceptibility measurements. The magnetocaloric properties of EuAu3Al2 were determined, and a magnetic entropy of ΔSM = -4.8 J kg(-1) K(-1) for a field change of 0 to 50 kOe was determined. Band structure calculations found that the f-bands of Eu present at the Fermi level of non-spin-polarized calculations are responsible for the ferromagnetic ordering in this phase, whereas COHP chemical bonding coupled with Bader charge analysis confirmed the description of the structure as covalently bonded polyanionic [Au3Al2](δ-) network interacting ionically with Eu(δ+).

Nb2RuB2 and Ta2RuB2 phases were recently predicted by GGA-VASP structure optimization to crystallize in the Nb2OsB2-type structure. Although the Fe-based (Mo2FeB2 type) and Os-based (Nb2OsB2 type, superstructure variant of Mo2FeB2 type) analogues have been synthesized and characterized successfully, the Ru-based phases remained unknown. Crystal structure prediction of Nb2RuB2 and Ta2RuB2 phases, using an evolutionary algorithm, led to the AlMn2B2-type structure in contrast to the aforementioned optimization; however, phonon calculations showed that the Nb2OsB2-type phases are dynamically more stable than the AlMn2B2-type phases. A slightly modified synthetic strategy finally led to the successful preparation of the predicted phases. The extremely quick arc-melting procedure, under argon atmosphere, not only led to a quantitative amount of the phases but also to single crystals suitable for structure determination. Powder and single-crystal X-ray diffraction as well as EDX analysis of the metal ratio have confirmed the GGA-VASP structure optimization: Nb2RuB2 and Ta2RuB2 compounds indeed crystallize isotypically with Nb2OsB2 structure, a superstructure variant of Mo2FeB2 type, in which B-dumbbells and Peierls-distorted Ru-chains are found. Susceptibility measurements on a Ta2RuB2 single crystal reveal no superconducting transition down to 2 K, even though some features in the band structures of both phases, similar to those reported in superconducting NbRuB, hinted at possible superconductivity.

Crystal orbital Hamilton population (COHP) bonding analysis has predicted that ScPd3 B0.5 is the least stable compound of the entire series Sc2 Ir6-x Pdx B. Here, we report a systematic study of Sc2 Ir6-x Pdx B (x=3, 5 and 6) by means of 11 B nuclear magnetic resonance (NMR), Knight shift (K) and nuclear spin-lattice relaxation rate (1/T1 ). NMR results combined with theoretical band structure calculations provide a measure of s- and non-s-character Fermi-level density of states. We present direct evidence that the enhanced s-state character of the Fermi level density of states (DOS) in ScPd3 B0.5 reduces the strength of the B 2p and Pd 4d hybridized states across the entire Sc2 Ir6-x Pdx B series. This hybridization strength relates to the opening of a deep pseudogap in the density of states of Sc2 IrPd5 B and the chemical bonding instability of ScPd3 B0.5 . This study is an experimental realization of a chemical fine-tuning of the electronic properties in intermetallic perovskites.

The new intermetallic compound Sr2Pd4Al5 was prepared from the elements by reaction in niobium ampoules. The structure was refined from single-crystal data, which indicate the formation of a new structure type in the orthorhombic crystal system [a = 1814.49(10), b = 431.64(4), c = 1102.47(4) pm] with space group Pnma (wR2 = 0.0251, 1666 F2 values, 68 parameters). Full ordering of the transition-metal and aluminum sites was observed. The compound can be described as a polar intermetallic phase with a polyanionic [Pd4Al5]δ– network; however, a quite unique bonding situation was found within this framework. In addition to the usual Pd–Al bonding, significant contributions to the stability of the framework caused by homoatomic Pd–Pd and Al–Al interactions can also be found. Structural relaxation confirmed the electronic stability and predicted the compound to be a metallic conductor.

The elastic properties of A 2 FeB 2 (A = Nb, Ta, Mo 2 FeB 2 -type structure) and their higher homologues A 2 OsB 2 and the predicted “A 2 RuB 2 ” (both with Nb 2 OsB 2 -type structure) have been investigated within the density functional theory (DFT) framework. Furthermore, the influence of magnetism, bonding and electronic structure on the elastic properties in the A 2 MB 2 series (A = Nb, Ta; M = Fe, Ru, Os) was studied. Ta 2 FeB 2 is predicted to order antiferromagnetically just like Nb 2 FeB 2 and Mo 2 FeB 2 . Magnetism affects the elastic properties of both Nb 2 FeB 2 and Ta 2 FeB 2 in a similar manner, but different from Mo 2 FeB 2 . We predict the ternary A 2 MB 2 (A = Nb, Ta; M = Ru, Os) diborides to have comparable mechanical properties as the binary hard and ultraincompressible diborides RuB 2 and OsB 2 . In general in these ternary diborides, the bulk modulus is heavily influenced by the strength of the chemical bonding (Integrated Crystal Orbital Hamilton Population: ICOHP) while the shear modulus is mainly affected by the position of the Fermi level in the density-of-states.

Detailed analytical studies of the solid solutions CeRu1–xNixSn revealed a sequence of three different structure types, CeRuSn, ZrNiAl, and TiNiSi, with increasing x value. All compounds have been synthesized and characterized by X-ray powder diffraction. The structures of CeRu0.68Ni0.32Sn, CeRu0.38Ni0.62Sn and CeRu0.14Ni0.86Sn have been refined from single crystal X-ray diffractometer data. The former one exhibits the ZrNiAl type, P 6 ¯ 2m, a = 737.9, c = 406.2 pm, wR2 = 0.0436, 345 F2 values, 17 variables. The two latter ones crystallize with the TiNiSi type, Pnma, a = 736.9, b = 468.5, c = 760.5 pm, wR2 = 0.0389, 631 F2 values, and a = 750.8, b = 461.8, c = 761.3 pm, wR2 = 0.0520, 632 F2 values, 21 variables for CeRu0.38Ni0.62Sn and CeRu0.14Ni0.86Sn, respectively. In accordance with magnetic susceptibility and Ce LIII-edge XANES measurements, cerium valence fluctuation has been proven for all samples that exhibit the hexagonal ZrNiAl type structure, while samples with the TiNiSi type show stable trivalent cerium. DFT calculations indicate that the CeRu0.5Ni0.5Sn composition should be thermodynamically stable in the hexagonal ZrNiAl type structure, while the unstable orthorhombic structure becomes monoclinic after structure relaxation.

The synergistic combination of experiment and density functional theory has led to the discovery of the first ferromagnetic material, Nb6Fe(1-x)Ir(6+x)B8, containing in its crystal structure iron chains embedded in stacked B6 rings. The strong ferromagnetic Fe-Fe interactions found in the iron chains induce an unexpected strengthening of the B-B interactions in the B6 rings. Beside these strong B-B interactions, strong interlayer metal-boron bonds (Ir-B and Nb-B) ensure the overall structural stability of this phase, while the magnetic Fe-Fe interactions are mainly responsible for the observed ferromagnetic ordering below T(C)=350 K.

The Nb2FeB2 phase (U3Si2-type, space group P4/mbm, no. 127) is known for almost 50 years, but until now its magnetic properties have not been investigated. While the synthesis of Nb2OsB2 (space group P4/mnc, no. 128, a twofold superstructure of U3Si2-type) with distorted Nb-layers and Os2-dumbbells was recently achieved, “Nb2RuB2” is still not synthesized and its crystal structure is yet to be revealed. Our first principles density functional theory (DFT) calculations have confirmed not only the experimental structures of Nb2FeB2 and Nb2OsB2, but also predict “Nb2RuB2” to crystalize with the Nb2OsB2 structure type. According to chemical bonding analysis, the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic M–B, B–Nb and M–Nb bonds (M=Fe, Ru, Os) are also found. These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of these ternary borides. The density-of-states at the Fermi level predicts metallic behavior, as expected, from metal-rich borides. Analysis of possible magnetic structures concluded preferred antiferromagnetic ordering for Nb2FeB2, originating from ferromagnetic interactions within iron chains and antiferromagnetic exchange interactions between them.

Powder samples and single crystals of the new ternary compound NbRuB were synthesized by arc-melting of the elements in a water-cooled crucible under an argon atmosphere. The samples have been characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy (EDX) measurements. Furthermore, the crystallographic, electronic, and bonding characteristics have been studied by density functional theory. The title compound crystallizes with a new orthorhombic structure type in the space group Pmma (no. 51) with the lattice parameters a = 10.870(2) A, b = 3.173(1) A, and c = 6.350(2) A. The structure consists of two kinds of atomic layers: the first layer (at y = 0) contains niobium atoms and isolated boron atoms, and the second (at y = 0.5) contains ruthenium atoms and boron dumbbells. Electronic structure relaxation has confirmed the crystallographic parameters, and crystal orbital Hamilton population (COHP) bonding analysis indicates that the B–B bond is the strongest bond, but the numerous and relatively strong metal–boron and Nb–Ru bonds are responsible for the overall stability and indicate a three-dimensional bonding character in the new compound.

The new ternary metal-rich boride, Nb{sub 2}OsB{sub 2}, was synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The compound was characterized from single-crystal X-ray data and EDX measurements. It crystallizes as a new superstructure (space group P4/mnc, no. 128) of the tetragonal U{sub 3}Si{sub 2}-structure type with lattice parameters a=5.922(1) A and c=6.879(2) A. All of the B atoms are involved in B{sub 2} dumbbells with B–B distances of 1.89(4) A. Structure relaxation using VASP (Vienna ab intio Simulation Package) has confirmed the space group and the lattice parameters. According to electronic structure calculations (TB–LMTO–ASA), the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic Os–B, Nb–B and Nb–Os bonds are also found: These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of this new phase. The density of state at the Fermi level predicts metallic behavior, as expected, from this metal-rich boride. - Graphical abstract: Nb{sub 2}OsB{sub 2} is, to the best of our knowledge, the first fully characterized phase in the ternary Nb–Os–B system. It crystallizes (space group P4/mnc, 128) with a new twofold superstructure of the U{sub 3}Si{sub 2} structure type (spacemore » group P4/mbm, 127), and is therefore the first boride in this structure family crystallizing with a superstructure of the U{sub 3}Si{sub 2} structure type. We show that the distortions leading to this superstructure occurs mainly in the Nb-layer, which tries to accommodate the large osmium atoms. The consequence of this puckering is the building osmium dumbbells instead of chains along [001]. - Highlights: • First compound in the Nb–Os–B system. • New twofold superstructure of U{sub 3}Si{sub 2} structure type. • Puckering of Nb-layer responsible for superstructure occurrence. • Chemical bonding studied by density functional theory.« less

The intermetallic compound EuAu3Al2 has been prepared by reaction of the elements in tantalum ampules. The structure was refined from single-crystal data, indicating that the title compound crystallizes in the orthorhombic crystal system (a = 1310.36(4), b = 547.87(1), c = 681.26(2) pm) with space group Pnma (wR2 = 0.0266, 1038 F(2) values, 35 parameters) and is isostructural to SrAu3Al2 (LT-SrZn5 type). Full ordering of the gold and aluminum atoms was observed. Theoretical calculations confirm that the title compound can be described as a polar intermetallic phase containing a polyanionic [Au3Al2](δ-) network featuring interconnected strands of edge-sharing [AlAu4] tetrahedra. Magnetic measurements and (151)Eu Mossbauer spectroscopic investigations confirmed the divalent character of the europium atoms. Ferromagnetic ordering below TC = 16.5(1) K was observed. Heat capacity measurements showed a λ-type anomaly at T = 15.7(1) K, in line with the ordering temperature from the susceptibility measurements. The magnetocaloric properties of EuAu3Al2 were determined, and a magnetic entropy of ΔSM = -4.8 J kg(-1) K(-1) for a field change of 0 to 50 kOe was determined. Band structure calculations found that the f-bands of Eu present at the Fermi level of non-spin-polarized calculations are responsible for the ferromagnetic ordering in this phase, whereas COHP chemical bonding coupled with Bader charge analysis confirmed the description of the structure as covalently bonded polyanionic [Au3Al2](δ-) network interacting ionically with Eu(δ+).

The new ternary transition metal-rich borides Ta2OsB2 and TaRuB have been successfully synthesized by arc-melting the elements in a water-cooled crucible under an argon atmosphere. The crystal structures of both compounds were solved by single-crystal X-ray diffraction and their metal compositions were confirmed by EDX analysis. It was found that Ta2OsB2 and TaRuB crystallize in the tetragonal Nb2OsB2 (space group P4/mnc, no. 128) and the orthorhombic NbRuB (space group Pmma, no. 51) structure types with lattice parameters a=5.878(2) A, c=6.857(2) A and a=10.806(2) A, b=3.196(1) A, c=6.312(2) A, respectively. Furthermore, crystallographic, electronic and bonding characteristics have been studied by density functional theory (DFT). Electronic structure relaxation has confirmed the crystallographic parameters while COHP bonding analysis indicates that B2-dummbells are the strongest bonds in both compounds. Moreover, the formation of osmium dumbbells in Ta2OsB2 through a Peierls distortion along the c-axis, is found to be the origin of superstructure formation. Magnetic susceptibility measurements reveal that the two phases are Pauli paramagnets, thus confirming the theoretical DOS prediction of metallic character. Also hints of superconductivity are found in the two phases, however lack of single phase samples has prevented confirmation. Furthermore, the thermodynamic stability of the two modifications of AMB (A=Nb, Ta; M =Ru, Os) are studied using DFT, as new possible phases containing either B4- or B2-units are predicted, the former being the most thermodynamically stable modification.

Crystal orbital Hamilton population (COHP) bonding analysis has predicted that ScPd

The new intermetallic compound Sr2Pd4Al5 was prepared from the elements by reaction in niobium ampoules. The structure was refined from single-crystal data, which indicate the formation of a new structure type in the orthorhombic crystal system [a = 1814.49(10), b = 431.64(4), c = 1102.47(4) pm] with space group Pnma (wR2 = 0.0251, 1666 F2 values, 68 parameters). Full ordering of the transition-metal and aluminum sites was observed. The compound can be described as a polar intermetallic phase with a polyanionic [Pd4Al5]δ– network; however, a quite unique bonding situation was found within this framework. In addition to the usual Pd–Al bonding, significant contributions to the stability of the framework caused by homoatomic Pd–Pd and Al–Al interactions can also be found. Structural relaxation confirmed the electronic stability and predicted the compound to be a metallic conductor.

The title compound is prepared from the elements (Nb tube, 1073 K, 7 d) and characterized by powder XRD, XPS, 27Al MAS NMR spectroscopy, magnetic measurements, and DFT band structure calculations.

DFT calculations for the ternary phases Sc2M6B (M: Ir, Pd, Ni) reveal the presence of pseudogaps near their Fermi levels between 61 and 68 valence electrons leading to the prediction of new phases Sc2Ir6-xPdxB and Sc2Ir6-xNixB (x = 0—6) in the double-perovskite-like Ti2Rh6B-type structure.

Analysis of the electronic density of states of the hypothetical ternary double-perovskite-like phases "Sc2T6B (T = Ir, Pd, Ni)" reveals the presence of deep and large pseudogaps between 61 and 68 valence electrons (VE) as well as a strong peak at 69 VEs. Subsequently, crystal orbital Hamilton population (COHP) bonding analysis shows that the heteroatomic T-B and Sc-T interactions are optimized in Sc2Ir6B (63 VE) but not in "Sc2Pd6B (69 VE)" and "Sc2Ni6B (69 VE)", thus indicating less stability for these VE-richer phases. These findings point out the possibility of discovering new double-perovskite-like borides through chemical substitution and lead to the study of the Sc2Ir6-xPdxB and Sc2Ir6-xNixB (x = 0-6; VE = 63-69) series, for which powder samples and single crystals were synthesized by arc melting the elements. Superstructure reflections were observed in the powder diffractograms of Sc2Ir6-xPdxB and Sc2Ir6-xNixB for x = 0-5 and VE = 63-68, thereby showing that these phases crystallize in the double-perovskite-like Ti2Rh6B-type structure (space group Fm3̅m, Z = 4). Single-crystal and Rietveld refinement results confirm and extend these findings because Pd (or Ni) is found to mix exclusively with Ir in all quaternary compositions. For x = 6, no superstructure reflections were observed, in accordance with the theoretical expectation for the 69 VE phases.

Highly crystalline Nb6Fe1-xIr6+xB8 (68% yield) is prepared from the elements in the molar ratio of Nb:Fe:Ir:B = 6:1:6:9 by rapid arc melting and quenching.

The new title compound is synthesized by arc melting of the elements in a water-cooled Cu crucible under argon (ratio 7:6:8 for Nb:Os:B, 80% yield).