Magnesium-rich intermetallic compounds Gd5Cu5Mg13 and Tb5Cu5Mg13 – intergrowth variants with CsCl and AlB2 related slabs

The magnesium-rich intermetallic compounds Gd5Cu5Mg13 and Tb5Cu5Mg13 were obtained from direct reactions of the elements (induction melting) in sealed tantalum ampoules. Both compounds crystallize with the orthorhombic Y5Cu5Mg13 type structure, space group Cmcm and Z = 4. The polycrystalline samples were characterized by powder X-ray diffraction. The structure of the gadolinium compound was refined from single crystal X-ray diffraction data: a = 414.78(2), b = 1921.87(12), c = 2573.89(16) pm, wR2 = 0.0492, 1611 F 2 values and 77 variables. Refinement of the occupancy parameters revealed a small degree of Gd/Mg mixing for the Gd3 site, leading to the composition Gd4.93(1)Cu5Mg13.07(1) for the studied crystal. The Gd5Cu5Mg13 structure contains slabs of equiatomic GdCuMg, which are embedded in a magnesium matrix. From a geometrical point of view, one can describe the Gd5Cu5Mg13 and Tb5Cu5Mg13 structures as intergrowth variants of distorted W/CsCl and AlB2 related slabs. The most remarkable crystal chemical feature concerns the bcc like magnesium slabs with short Mg–Mg distances ranging from 300 to 342 pm. Temperature dependent magnetic susceptibility measurements show Curie-Weiss paramagnetism for Tb5Cu5Mg13 (10.5(1) μ B Tb atom−1 and Θ P = −11.6(1) K). Antiferromagnetic ordering was detected below the Néel temperatures of T N = 30.5(3) K.

Magnesium and barium in two substructures: BaTMg2 (T = Pd, Ag, Pt, Au) and the isotypic cadmium compound BaAuCd2 with MgCuAl2 type structure

The intermetallic barium compounds BaTMg2 (T = Pd, Ag, Pt, Au) and BaAuCd2 were synthesized by reactions of the elements in sealed tantalum ampoules in muffle furnaces. The five compounds crystallize with the orthorhombic MgCuAl2 type structure, space group Cmcm, with small differences in chemical bonding between the magnesium and cadmium series. All samples were characterized through their Guinier powder diffraction patterns. The structures of BaPdMg2 (a = 444.57(4), b = 1174.67(10), c = 827.58(7) pm, wR2 = 0.0460, 475 F 2 values, 16 variables), BaAuMg2 (a = 450.27(6), b = 1183.94(16), c = 838.76(11) pm, wR2 = 0.0355, 473 F 2 values, 16 variables) and BaAuCd2 (a = 463.31(5), b = 1112.79(12), c = 826.63(8) pm, wR2 = 0.0453, 469 F 2 values, 16 variables) were refined from single crystal X-ray diffraction data. The large barium atoms push the [TMg2] respectively [AuCd2] substructures apart. This allows fast moisture attack and leads to fast hydrolyzes of the samples when they get in contact with water. The influence of the difference in electronegativity between magnesium and cadmium is reflected for the pair of compounds BaAuMg2 and BaAuCd2. The magnesium compound shows the higher auridic character, while the cadmium compound shows a tendency towards a three-dimensional cadmium substructure.

Intermetallic compounds RE 2Ga2Mg (RE = Tb–Tm, Lu) with Mo2B2Fe-type structure

The rare earth intermetallic compounds RE 2Ga2Mg with RE = Tb–Tm and Lu were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. These rare earth-rich phases crystallize with the tetragonal Mo2B2Fe-type structure, space group P4/mbm and Z = 2. The polycrystalline samples were characterized through their Guinier powder patterns. The structures of Er2Ga2.092(1)Mg0.908(1), Tm2Ga2.037(1)Mg0.963(1) and Lu2Ga2.176(1)Mg0.824(1) have been refined from single crystal X-ray diffractometer data. The refinements revealed small homogeneity ranges (small degrees of Mg/Ga mixing on the 2a sites). The magnesium atoms show square planar coordination by Ga2 dumbbells (282 pm Mg–Ga and 257 pm Ga–Ga in the lutetium compound). Geometrically one can describe the RE 2Ga2Mg phases as 1:1 intergrowth structures of CsCl and AlB2-related slabs of compositions REMg and REGa2. From DFT based calculations, charge transfer from the rare earth and magnesium atoms towards gallium can be illustrated in electron localization function ELF slice planes showing strong localization around gallium in the basal plane as well as along the tetragonal c axis signaling Ga–Ga pair interactions. The site-projected density of states DOS and COOP data further quantify this observation. Temperature dependent magnetic susceptibility measurements show Pauli paramagnetism for Sc2Ga2Mg and Lu2Ga2Mg with low room temperature susceptibility values of 2.1(1) × 10−4 and 1.1(1) × 10−4 emu mol−1, respectively. Ho2Ga2Mg, Er2Ga2Mg and Tm2Ga2Mg are Curie-Weiss paramagnets with stable trivalent rare earth ground states. Antiferromagnetic ordering was detected below the Néel temperatures of T N = 18.6(1) (RE = Ho), 11.9(1) (RE = Er) and 6.4(1) K (RE = Tm). The three compounds show metamagnetic transitions in their 3 K magnetization isotherms. Tm2Ga2Mg exhibits a square loop behavior with small hysteresis.

EuTMg2 (T = Pd, Ag, Ir, Pt, Au), EuTCd2 (T = Pd, Pt, Au) and CaRhMg2 – intermetallic compounds with orthorhombically distorted tetrahedral magnesium (cadmium) substructures

The magnesium- and cadmium-rich intermetallic phases EuTMg2 (T = Rh, Pd, Ag, Ir, Pt, Au), EuTCd2 (T = Pd, Pt, Au) and CaRhMg2 were synthesized from the elements in sealed niobium or tantalum ampoules and with heat treatments in muffle or induction furnaces. The samples were characterized by powder X-ray diffraction and the structures were refined from single crystal X-ray diffractometer data. EuTMg2 (T = Pd, Ag, Pt, Au) and EuTCd2 (T = Pd, Pt, Au) crystallize with the MgCuAl2 type, space group Cmcm, while EuRhMg2, EuIrMg2 and CaRhMg2 adopt the YSiPd2 type, space group Pnma. The striking crystal chemical motif of both series of compounds are networks of puckered Mg(Cd) hexagons in ABAB stacking sequence that derive from the aristotype AlB2; however, with different tiling. Temperature dependent magnetic susceptibility and 151Eu Mössbauer spectroscopic measurements indicate stable divalent europium. Antiferromagnetic ordering sets in at 20.2 (EuIrMg2), 22.3 (EuPdMg2), 21.3 (EuAgMg2), 10.9 (EuPdCd2) and 15.5 K (EuPtCd2), respectively. The stable antiferromagnetic ground states are substantiated by metamagnetic transitions. The 151Eu isomer shifts show a linear correlation with the valence electron count for the whole series of EuTMg2, EuTCd2, EuTIn2 and EuTSn2 phases.

Revealing the Bonding Nature in an ALnZnTe3-Type Alkaline-Metal (A) Lanthanide (Ln) Zinc Telluride by Means of Experimental and Quantum-Chemical Techniques

Tellurides have attracted an enormous interest in the quest for materials addressing future challenges, because many of them are at the cutting edge of basic research and technologies due to their remarkable chemical and physical properties. The key to the tailored design of tellurides and their properties is a thorough understanding of their electronic structures including the bonding nature. While a unique type of bonding has been recently identified for post-transition-metal tellurides, the electronic structures of tellurides containing early and late-transition-metals have been typically understood by applying the Zintl−Klemm concept; yet, does the aforementioned formalism actually help us in understanding the electronic structures and bonding nature in such tellurides? To answer this question, we prototypically examined the electronic structure for an alkaline metal lanthanide zinc telluride, i.e., RbDyZnTe3, by means of first-principles-based techniques. In this context, the crystal structures of RbLnZnTe3 (Ln = Gd, Tb, Dy), which were obtained from high-temperature solid-state syntheses, were also determined for the first time by employing X-ray diffraction techniques.

Cd2 and Co2 dumbbell formation in the yttrium-rich intermetallic compounds Y14Ni3Cd3 and Y6Co2Zn

The yttrium-rich intermetallic compounds Y14Ni3Cd3 and Y6Co2Zn were obtained by direct reactions of the elements in sealed tantalum tubes in an induction furnace. Both samples were characterized by X-ray powder diffraction and the structures were refined from single-crystal X-ray diffraction data: Lu14Co3In3 type, P42/nmc, a = 960.06(5), c = 2314.9(1) pm, wR2 = 0.0669, 2034 F 2 values, 63 parameters for Y14Ni3.16(2)Cd2.84(2) and Ho6Co2Ga type, Immm, a = 943.08(7), b = 950.08(7), c = 997.64(7) pm, wR2 = 0.0476, 981 F 2 values, 34 parameters for Y6Co2Zn. One cadmium site shows a small degree of Cd/Ni mixing, leading to the composition Y14Ni3.16(2)Cd2.84(2). Although both compounds crystallize with significantly different structure types, they show very similar monomeric building units: (i) transition metal centered trigonal prisms of yttrium, (ii) empty Y6 octahedra and (iii) icosahedral coordination of the cadmium respectively zinc atoms. The condensation patterns of these building units are discussed and for Y14Ni3.16(2)Cd2.84(2), we elaborate a crystal chemical building principle along with the rare earth metal-rich phases RE 15Rh5Cd2 (La15Rh5Cd2 type), RE 23 T 7 X 4 (Pr23Ir7Mg4 type), RE 4 TX (Gd4RhMg type) and RE 10 TX 3/RE 9 TX 4 (ordered Co2Al5 versions). The structures of Y14Ni3Cd3 and Y6Co2Zn show dumbbell formation: 306 pm Cd–Cd in Y14Ni3Cd3 and 224 pm Co1–Co1 and 246 pm Co2–Co2 in Y6Co2Zn.

Alkaline earth metal ordering in CaCu9Mg2 and SrCu9Mg2

The copper-rich intermetallic compounds CaCu9Mg2 and SrCu9Mg2 were synthesized by induction melting of the elements and subsequent annealing in a muffle furnace. CaCu9Mg2 and SrCu9Mg2 crystallize with the TbCu9Mg2 type structure, space group P 63/mmc, which is a ternary ordered variant of CeNi3. The polycrystalline samples were characterized through their X-ray powder patterns. The CaCu9Mg2 structure was refined from single-crystal X-ray diffraction data. a = 504.13(9), c = 1622.5(3) pm, wR2 = 0.0635, 302 F2 values and 19 variables. The two striking coordination polyhedra in the CaCu9Mg2 structure are Ca@Cu18Mg2 and Mg@Cu12Mg3Ca. These polyhedra condense to layers which are stacked in ABA′B′ sequence. The X-ray data give no hint for Ca/Mg mixing.

Squares of gold atoms and linear infinite chains of Cd atoms as building units in the intermetallic phases REAu4Cd2 (RE=La–Nd, Sm) with YbAl4Mo2-type structure

The gold-rich intermetallic compounds REAu4Cd2 (RE = La–Nd, Sm) were synthesized from the elements in sealed tantalum ampoules. Their characterization by X-ray powder and single crystal data confirmed the tetragonal YbAl4Mo2 type, space group I4/mmm. The basic building units are Au4 squares (278 pm Au–Au in CeAu4Cd2) and infinite linear cadmium chains (275 pm Cd–Cd in CeAu4Cd2). We exemplarily studied the solid solution CeAu4+ x Cd2− x for x = 0–1 up to CeAu5Cd. Electron diffraction patterns on a CeAu5Cd sample confirm the single crystal data. They give no hint for complete gold-cadmium ordering. Temperature-dependent magnetic susceptibility measurements of CeAu4Cd2, CeAu5Cd, PrAu4Cd2 and NdAu4Cd2 show stable trivalent rare earth ions and give no hint for magnetic ordering above 3 K.

Osmium and magnesium: structural segregation in the rare earth-rich intermetallics RE 4OsMg (RE=La–Nd, Sm) and RE 9 TMg4 (RE=Gd, Tb)

Ternary rare earth metal-rich intermetallic phases containing osmium and magnesium were obtained by induction melting of the elements in sealed niobium ampoules under argon followed by annealing in muffle furnaces. The large rare earth elements form the series of Gd4RhIn-type (F4̅3m) intermetallics RE 4OsMg with RE = La–Nd and Sm, while the smaller rare earth metals gadolinium and terbium form the Y9CoMg4-type (P63/mmc) phases Gd9OsMg4 and Tb9OsMg4. All samples were characterized by X-ray powder diffraction (Guinier technique). The structures of Ce4Os0.973Mg1.027 (a = 1406.54(7) pm, wR2 = 0.0478), Nd4Os0.978Mg1.022 (a = 1402.00(7) pm, wR2 = 0.0463), Sm4Os0.920Mg1.080 (a = 1387.33(5) pm, wR2 = 0.0378) and Gd9OsMg4 (a = 971.01(5), c = 980.43(5) pm, wR2 = 0.0494) were refined from single-crystal X-ray diffractometer data. The three RE 4OsMg phases show small degrees of Os/Mg mixing, as is frequently observed for Rh/In in Gd4RhIn-type intermetallics. The basic building units in both structures are osmium-centered RE 6 trigonal prisms that are condensed with empty RE 6 octahedra. The magnesium atoms in both types build Mg4 tetrahedra. The latter are isolated (312 pm Mg–Mg in Ce4OsMg) and incorporated within the three-dimensional network of prisms and octahedra in the RE 4OsMg phases while one observes rows of corner- and face-sharing tetrahedra in Gd9OsMg4 (305 and 314 pm Mg–Mg). In both structure types direct Os–Mg bonding is not observed.

Rare earth-rhodium-plumbides RE 2Rh2Pb with RE = La–Nd, Sm, Gd and Tb

The plumbides RE 2Rh2Pb (RE = La–Nd, Sm, Gd, Tb) were synthesized in sealed niobium ampoules by induction melting of the pure elements or directly via arc-melting. The characterization of the samples by X-ray powder diffraction confirmed their Mo2B2Fe-type structure (space group P4/mbm) at room temperature. The Sm2Rh1.924Pb structure was refined from single-crystal X-ray diffractometer data: a=760.02(5), c=378.20(3) pm, wR=0.0387, 292 F 2 values, 13 variables. The rhodium site shows small defects. The RE 2Rh2Pb plumbides are simple 1:1 intergrowth structures of AlB2 and CsCl related slabs of compositions RERh2 and REPb. The Rh2 dumbbell in the SmRh2 slab of Sm2Rh2Pb shows a Rh–Rh distance of 281 pm. Temperature-dependent magnetic susceptibility measurements of La2Rh2Pb, Pr2Rh2Pb and Nd2Rh2Pb showed that the rhodium atoms carry no localized magnetic moments. La2Rh2Pb exhibits Pauli-paramagnetic behavior induced by the conduction electrons. The ground state of the praseodymium compound is ferromagnetic below T C=3.3 K while the neodymium compound shows a transition to an antiferromagnetic state at T N=6.1 K and a metamagnetic transition at a critical field of ca. 1000 Oe.

Magnetic and magnetocaloric properties of the coloured Heusler phases GdAg2Mg and REAgAuMg (RE=Gd, Tb, Dy)

The magnetocaloric effect (MCE) of the ferromagnetic compound GdAg2Mg [T C=98.3(5) K] was investigated along with its electrical resistivity and the specific heat capacity. The magnetic entropy changes (–ΔS M) as well as the changes in adiabatic temperature (ΔT ad) have been calculated from these data. Furthermore, the magnetic susceptibility of the pseudo-quaternary Heusler phases GdAgAuMg, TbAgAuMg and DyAgAuMg [i.e. RE(Ag0.5Au0.5)2Mg] were measured and compared to the data for the pure silver and gold compounds REAg2Mg and REAu2Mg. The substitution of the transition metal at the crystallographic Wyckoff site 8c influences the magnetic ground state of the trivalent rare earth metals and therefore drastically alters the Curie temperatures. The structure of GdAgAuMg was refined from single crystal X-ray diffraction data, revealing a small deviation from the equiatomic composition leading to the refined formula GdAg0.92(6)Au1.08(6)Mg [space group Fm3̅m, Z=4, a=695.03(10) pm, wR2=0.0883, 55 F 2 values, six parameters]. The intermetallic compounds were synthesised in sealed niobium ampoules under high temperature conditions. They have reddish to brassy colour.

Rare earth-rich cadmium compounds RE 10 TCd3 (RE=Y, Tb, Dy, Ho, Er, Tm, Lu; T=Rh, Pd, Ir, Pt) with an ordered Co2Al5-type structure

Eighteen new rare earth-rich intermetallic phases RE 10 TCd3 (RE=Y, Tb, Dy, Ho, Er, Tm, Lu; T=Rh, Pd, Ir, Pt) were obtained by induction melting of the elements in sealed niobium ampoules followed by annealing in muffle furnaces. All samples were characterized by X-ray powder diffraction. The structures of four representatives were refined from single-crystal X-ray diffractometer data: ordered Co2Al5 type, P63/mmc, a=951.2(1), c=962.9(2) pm, wR=0.0460, 595 F 2 values, 20 parameters for Er10RhCd3; a=945.17(4), c=943.33(4), wR=0.0395, 582 F 2 values, 21 parameters for Lu9.89PdCd3.11; a=964.16(6), c=974.93(6) pm, wR=0.0463, 614 F 2 values, 21 parameters for Y10Ir1.09Cd2.91; a=955.33(3), c=974.56(3) pm, wR=0.0508, 607 F 2 values, 22 refined parameters for Dy9.92IrCd3.08. Refinements of the occupancy parameters revealed small homogeneity ranges resulting from RE/Cd, respectively T/Cd mixing. The basic building units of the RE 10 TCd3 phases are transition metal-centered RE 6 trigonal prisms (TP) that are condensed with double-pairs of empty RE 6 octahedra via common triangular faces. A second type of rods is formed by slightly distorted RE3@Cd6 RE 6 icosahedra which are condensed via Cd3 triangular faces. The shortest interatomic distances occur for RE–T, compatible with strong covalent bonding interactions. Temperature dependent magnetic susceptibility measurements were performed for RE 10RhCd3 (RE=Dy–Tm, Lu), RE 10IrCd3 (RE=Er, Tm, Lu) and RE 10PtCd3 (RE=Y, Lu). While Y10PtCd3 and Lu10 TCd3 (T=Rh, Ir, Pt) show Pauli paramagnetic behavior, the compounds containing paramagnetic rare earth elements show Curie-Weiss behavior (the experimental magnetic moments indicate stable trivalent RE 3+) and magnetic ordering at low temperatures: T C=80.5 K for Dy10RhCd3 and Neél temperatures of 42.1, 23.3, 12.6, 5.9, 10.0 K for Ho10RhCd3, Er10RhCd3, Er10IrCd3, Tm10RhCd3, Tm10IrCd3, respectively.

GdCuMg with ZrNiAl-type structure – an 82.2 K ferromagnet

GdCuMg has been synthesized by induction-melting of the elements in a sealed niobium ampoule followed by annealing in a muffle furnace. The sample was studied by powder and single crystal X-ray diffraction: ZrNiAl type, P6̅2m (a=749.2(4), c=403.3(1) pm), wR2=0.0242, 315 F 2 values and 15 variables. Temperature dependent magnetic susceptibility measurements have revealed an experimental magnetic moment of 8.54(1) μB per Gd atom. GdCuMg orders ferromagnetically below T C=82.2(5) K and based on the magnetization isotherms it can be classified as a soft ferromagnet.

Excellent magnetocaloric properties in RE2Cu2Cd (RE = Dy and Tm) compounds and its composite materials

The magnetic properties and magnetocaloric effect (MCE) of ternary intermetallic RE₂Cu₂Cd (RE = Dy and Tm) compounds and its composite materials have been investigated in detail. Both compounds undergo a paramagnetic to ferromagnetic transition at its own Curie temperatures of T_C ~ 48.5 and 15 K for Dy₂Cu₂Cd and Tm₂Cu₂Cd, respectively, giving rise to the large reversible MCE. An additionally magnetic transition can be observed around 16 K for Dy₂Cu₂Cd compound. The maximum values of magnetic entropy change (−ΔS_M^max) are estimated to be 17.0 and 20.8 J/kg K for Dy₂Cu₂Cd and Tm₂Cu₂Cd, for a magnetic field change of 0–70 kOe, respectively. A table-like MCE in a wide temperature range of 10–70 K and enhanced refrigerant capacity (RC) are achieved in the Dy₂Cu₂Cd - Tm₂Cu₂Cd composite materials. For a magnetic field change of 0–50 kOe, the maximum improvements of RC reach 32% and 153%, in comparison with that of individual compound Dy₂Cu₂Cd and Tm₂Cu₂Cd. The excellent MCE properties suggest the RE₂Cu₂Cd (RE = Dy and Tm) and its composite materials could be expected to have effective applications for low temperature magnetic refrigeration.

Magnetic properties of RE 10 TCd3 (RE = Ho, Er, Tm, Lu; T = Fe, Co, Ni, Ru) and 57Fe Mössbauer spectroscopic data of Y10FeCd3

Fourteen X-ray-pure intermetallic compounds RE 10 TCd3 (RE = Ho, Er, Tm, Lu; T = Fe, Co, Ni, Ru) and Y10FeCd3 were obtained through high-frequency melting of the elements in sealed niobium tubes and subsequent annealing in a muffle furnace. They adopt the Er10FeCd3 structure, a ternary ordered version of the Co2Al5 type. Temperature-dependent magnetic susceptibility measurements show Pauli paramagnetism for the lutetium compounds Lu10FeCd3, Lu10CoCd3, and Lu10RuCd3. The RE 10 TCd3 phases with holmium, erbium, and thulium show Curie–Weiss paramagnetism and the experimental magnetic moments match with the free ion values of RE 3+. All these compounds order antiferromagnetically. The highest Néel temperature was observed for the holmium compounds, e.g. 46.5 K for Ho10RuCd3. Some of the RE 10 TCd3 phases show field-induced spin reorientations. A 57Fe Mössbauer spectrum of Y10FeCd3 confirms the single crystallographic iron site.

Ternary aurides RE 4Mg3Au10 (RE = La, Ce, Pr) and RE 4Cd3Au10 (RE = Y, La–Nd, Sm, Gd–Dy) – ordering variants of the Zr7Ni10 type

The intermetallic gold compounds RE 4Mg3Au10 (RE = La, Ce, Pr) and RE 4Cd3Au10 (RE = Y, La–Nd, Sm, Gd–Dy) were obtained from the elements through high-frequency melting in sealed niobium tubes and subsequent annealing in a muffle furnace. The new aurides crystallize with the Ca4In3Au10-type structure. They were characterized through Guinier powder patterns. The structures of Pr4.46Cd2.54Au10 and Tb4.38Cd2.62Au10 were refined from single crystal X-ray diffractometer data: Cmce, a = 1396.73(6), b = 1009.38(3), c = 1019.51(3) pm, wR2 = 0.0423, 1281 F 2 values, 47 variables for Pr4.46Cd2.54Au10 and a = 1362.68(3), b = 995.52(4), c = 1003.79(3) pm, wR2 = 0.0381, 1594 F 2 values, F 2 47 variables for Tb4.38Cd2.62Au10. The 8e sites of both crystals show substantial Cd/Pr respectively Cd/Tb mixing, indicating small homogeneity ranges for all RE 4+x Mg3–x Au10 and RE 4+x Cd3–x Au10 aurides. The gold atoms in these aurides form a pronounced two-dimensional substructure (275–327 pm Au–Au in Pr4.46Cd2.54Au10) which encages the Mg1/Cd1 (coordination number 8) and RE2 (coordination number 11) atoms. These blocks are separated by the Mg2/Cd2 and RE1 atoms with an intergrowth of Mg2/Cd2@Au8 and RE1@Au10 polyhedra. Temperature dependent magnetic susceptibility and specific heat measurements of Tb4Cd3Au10 have shown antiferromagnetic ordering at a Néel temperature of 12(1) K.