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The novel quaternary thiogermanate Li4CdGe2S7 (tetralithium cadmium digermanium heptasulfide) was discovered from a solid‐state reaction at 750 °C. Single‐crystal X‐ray diffraction data were collected and used to solve and refine the structure. Li4CdGe2S7 is a member of the small, but growing, class of I4–II–IV2–VI7 diamond‐like materials. The compound adopts the Cu5Si2S7 structure type, which is a derivative of lonsdaleite. Crystallizing in the polar space group Cc, Li4CdGe2S7 contains 14 crystallographically unique ions, all residing on general positions. Like all diamond‐like structures, the compound is built of corner‐sharing tetrahedral units that create a relatively dense three‐dimensional assembly. The title compound is the major phase of the reaction product, as evidenced by powder X‐ray diffraction and optical diffuse reflectance spectroscopy. While the compound exhibits a second‐harmonic generation (SHG) response comparable to that of the AgGaS2 (AGS) reference material in the IR region, its laser‐induced damage threshold (LIDT) is over an order of magnitude greater than AGS for λ = 1.064 µm and τ = 30 ps. Bond valence sums, global instability index, minimum bounding ellipsoid (MBE) analysis, and electronic structure calculations using density functional theory (DFT) were used to further evaluate the crystal structure and electronic structure of the compound and provide a comparison with the analogous I2–II–IV–VI4 diamond‐like compound Li2CdGeS4. Li4CdGe2S7 appears to be a better IR nonlinear optical (NLO) candidate than Li2CdGeS4 and one of the most promising contenders to date. The exceptional LIDT is likely due, at least in part, to the wider optical bandgap of ∼3.6 eV. [ABSTRACT FROM AUTHOR]

The new compounds Li2Mg2Si2S6 and Li2Mg2Ge2S6 have been prepared via traditional high‐temperature, solid‐state synthesis. The title compounds crystallize in the polar, noncentrosymmetric, trigonal space group P31m (No. 157) and adopt a new structure type featuring staggered, ethane‐like (T2S6)6− units, where T=Si or Ge. These (T2S6)6− units are nestled within the holes of magnesium‐sulfide "layers" that are created through the edge‐sharing of MgS6 octahedra. The holes found in the lithium‐sulfide "layers", created by LiS6 edge‐sharing octahedra, remain vacant, containing no (T2S6)6− anionic group. Through the face sharing of the respective MgS6 and LiS6 octahedra, the magnesium‐sulfide and lithium‐sulfide "layers" are stitched together resulting in an overall three‐dimensional structure. The optical bandgaps of Li2Mg2Si2S6 and Li2Mg2Ge2S6 are 3.24 and 3.18 eV, respectively, as estimated from optical diffuse reflectance UV‐Vis‐NIR spectroscopy. The compounds exhibit second harmonic generation responses of ∼0.24×KDP and ∼2.92×α‐quartz for Li2Mg2Si2S6 and ∼0.17×KDP and ∼2.08×α‐quartz for Li2Mg2Ge2S6, using a Nd:YAG laser at 1.064 μm. Electronic structure calculations were performed using density functional theory and the linearized augmented plane‐wave approach within the WIEN2k software package. Examination of the electronic band structures shows that these compounds are indirect bandgap semiconductors. [ABSTRACT FROM AUTHOR]

The new quaternary thiosilicate, Li2PbSiS4 (dilithium lead silicon tetrasulfide), was prepared in an evacuated fused‐silica tube via high‐temperature, solid‐state synthesis at 800 °C, followed by slow cooling. The crystal structure was solved and refined using single‐crystal X‐ray diffraction data. By strict definition, the title compound crystallizes in the stannite structure type; however, this type of structure can also be described as a compressed chalcopyrite‐like structure. The Li+ cation lies on a crystallographic fourfold rotoinversion axis, while the Pb2+ and Si4+ cations reside at the intersection of the fourfold rotoinversion axis with a twofold axis and a mirror plane. The Li+ and Si4+ cations in this structure are tetrahedrally coordinated, while the larger Pb2+ cation adopts a distorted eight‐coordinate dodecahedral coordination. These units join together via corner‐ and edge‐sharing to create a dense, three‐dimensional structure. Powder X‐ray diffraction indicates that the title compound is the major phase of the reaction product. Electronic structure calculations, performed using the full potential linearized augmented plane wave method within density functional theory (DFT), indicate that Li2PbSiS4 is a semiconductor with an indirect bandgap of 2.22 eV, which compares well with the measured optical bandgap of 2.51 eV. The noncentrosymmetric crystal structure and relatively wide bandgap designate this compound to be of interest for IR nonlinear optics. [ABSTRACT FROM AUTHOR]

Abstract The series of quaternary rare-earth phosphides RE MnCuP 2 (RE = Y, La–Nd, Sm, Gd–Tm, Lu), which had previously been limited to the Yb member, has been prepared by reaction of the elements at 800 °C. These phosphides adopt the CaAl 2 Si 2 -type structure (trigonal, space group P 3 ¯ m 1 , Z = 1) with Mn and Cu atoms disordered over the tetrahedral M sites within [ M 2 P 2 ] slabs. However, single-crystal X-ray diffraction studies, carried out on some of these members (RE = Tb, Dy, Er, Tm), provide evidence for an interstitial octahedral site being partially occupied by Cu atoms, resulting in the nonstoichiometric formulation RE MnCu 1+ x P 2 (x = 0.10–0.16). A second polymorph of LaMnCuP 2 adopting the BaCu 2 S 2 -type structure (orthorhombic, space group Pnma , Z = 4) was also identified in the course of these investigations. Electronic structure calculations on a ordered superstructure model of YMnCuP 2 indicate the absence of a band gap. Graphical abstract RE MnCuP 2 with CaAl 2 Si 2 -type structure forms for nearly all RE members, and LaMnCuP 2 forms an additional BaCu 2 S 2 -type polymorph. fx1 Highlights • Phosphides RE MnCuP 2 with CaAl 2 Si 2 -type structure were prepared for nearly all RE. • Slight excess of Cu atoms can be accommodated in interstitial octahedral sites. • LaMnCuP 2 forms a second polymorph with BaCu 2 S 2 -type structure. • Calculations on YMnCuP 2 indicate absence of band gap. [ABSTRACT FROM AUTHOR]

The four ternary arsenides ATt 3 As 3 ( A =K, Rb; Tt =Ge, Sn) were obtained by reaction of the elements at 600–650 °C. They adopt an orthorhombic structure (space group Pnma , Z =4, with cell parameters ranging from a =9.9931(11) Å, b =3.7664(4) Å, c =18.607(2) Å for KGe 3 As 3 to a =10.3211(11) Å, b =4.0917(4) Å, c =19.570(2) Å for RbSn 3 As 3 ) containing corrugated [ Tt 3 As 3 ] layers built from Tt -centred trigonal pyramids and tetrahedra forming five-membered rings decorated with As handles. They can be considered to be Zintl phases with Tt atoms in +4, +3, and +1 oxidation states. Band structure calculations predict that these compounds are semiconductors with narrow band gaps (0.71 eV in KGe 3 As 3 , 0.50 eV in KSn 3 As 3 ). [ABSTRACT FROM AUTHOR]

The new ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. The compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared ALPN4 and GaPn4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[TR3+][Pn3-]3, or rather [AE2+]6[Tr2+]Tr2Pn6]12-, i.e., as Zintl phases. [ABSTRACT FROM AUTHOR]

Abstract: Three series of quaternary rare-earth transition-metal pnictides REMM′Pn 2 (M=Cu, Ag; M′=Zn; Pn=P, As) have been prepared by reaction of the elements at 800°C, with crystal growth promoted through the addition of iodine. The extent of RE substitution is broad in these series: RECuZnAs2 (RE=Y, La Nd, Sm, Gd–Lu), REAgZnP2 (RE=La–Nd, Sm, Gd–Dy), and REAgZnAs2 (RE=La Nd, Sm, Gd Dy). Powder and single-crystal X-ray diffraction analysis revealed that they adopt the trigonal CaAl2Si2-type structure (space group P m1, Z=1), in which Cu or Ag atoms are disordered with Zn atoms over the unique tetrahedrally coordinated transition-metal site. Magnetic measurements indicated Curie–Weiss behavior for several members of the RECuZnAs2 and REAgZnP2 series. Core-line X-ray photoelectron spectra (XPS) collected on some RECuZnAs2 members corroborate the charge assignment deduced by the Zintl concept for these compounds, (RE 3+)(M 1+)(Zn2+)(Pn 3−)2. Optical diffuse reflectance spectra and valence band XPS spectra established that these compounds are small band-gap semiconductors (up to ~0.8eV in REAgZnP2) or semimetals (RECuZnAs2). Band structure calculations also support this electronic structure and indicate that the band gap can be narrowed through appropriate chemical substitution (RE=smaller atoms, M=Cu, and Pn=As). [Copyright &y& Elsevier]

Six series of quaternary rare-earth transition-metal chalcogenides RE 3 MGaCh 7 (M=Fe, Co, Ni; Ch=S, Se), comprising 33 compounds in total, have been prepared by reactions of the elements at 1050°C (for the sulphides) or 900°C (for the selenides). They adopt noncentrosymmetric hexagonal structures (ordered Ce3Al1.67S7-type, space group P63, Z=2) with cell parameters in the ranges of a=9.5–10.2Å and c=6.0–6.1Å for the sulphides and a=10.0–10.5Å and c=6.3–6.4Å for the selenides as refined from powder X-ray diffraction data. Single-crystal structures were determined for five members of the sulphide series RE 3FeGaS7 (RE=La, Pr, Tb) and RE 3CoGaS7 (RE=La, Tb). The highly anisotropic crystal structures consist of one-dimensional chains of M-centred face-sharing octahedra and stacks of Ga-centred tetrahedra all pointing in the same direction. Magnetic measurements on the sulphides reveal paramagnetic behaviour in some cases and long-range antiferromagnetic behaviour with low Néel temperatures (15K or lower) in others. Ga L-edge XANES spectra support the presence of highly cationic Ga tetrahedral centres with a tendency towards more covalent Ga–Ch character on proceeding from the sulphides to the selenides. Band structure calculations on La3FeGaS7 indicate that the electronic structure is dominated by Fe 3d-based states near the Fermi level. [ABSTRACT FROM AUTHOR]

Six quaternary rare-earth-containing sulphides RE 3 MInS7 (M=Fe, Co, Ni) have been prepared by reactions of the elements at 1050–1150°C. They are the first examples of chalcogenides RE 3 MM'Ch 7 adopting related La3CuSiS7- or ordered Ce3Al1.67S7-type structures in which the M' component is indium. They crystallize in the noncentrosymmetric hexagonal space group P63 with Z=2 and cell parameters in the ranges of a=9.95–10.15Å and c=6.25–6.29Å for RE 3FeInS7 (RE=La–Pr), RE 3CoInS7 (RE=La, Ce), and La3NiInS7. The crystal structure consists of parallel chains of face-sharing M-centred octahedra and stacks of In-centred tetrahedra, all pointing in the same polar direction, with seven-coordinate La atoms in the intervening spaces. X-ray photoelectron spectra support the valence assignments implied by the formulation (RE 3+)3(M 2+)(In3+)(S2−)7. Magnetic measurements are suggestive of antiferromagnetic coupling between the M moments. Band structure calculations reveal that a band gap of 0.25eV is present in La3FeInS7, whereas the increased electron count in La3CoInS7 and La3NiInS7 causes the Fermi level to cut narrow bands. [ABSTRACT FROM AUTHOR]

Through arc-melting reactions of the elements and annealing at 800°C, the ternary rare-earth germanides RE 3Ru2Ge3 and RE 3Ir2Ge3 have been prepared for most of the smaller RE components (RE=Y, Gd–Tm, Lu). In the iridium-containing reactions, the new phases RE 2IrGe2 were also generally formed as by-products. Powder X-ray diffraction revealed orthorhombic Hf3Ni2Si3-type structures (space group Cmcm, Z=4) for RE 3 M 2Ge3 (M=Ru, Ir) and monoclinic Sc2CoSi2-type structures (space group C2/m, Z=4) for RE 2IrGe2. Full crystal structures were determined by single-crystal X-ray diffraction for all members of RE 3Ru2Ge3 (a=4.2477(6)Å, b=10.7672(16)Å, c=13.894(2)Å for RE=Y; a=4.2610(3)–4.2045(8)Å, b=10.9103(8)–10.561(2)Å, c=14.0263(10)–13.639(3)Å in the progression of RE from Gd to Lu) and for Tb3Ir2Ge3 (a=4.2937(3)Å, b=10.4868(7)Å, c=14.2373(10)Å). Both structures can be described in terms of CrB- and ThCr2Si2-type slabs built from Ge-centred trigonal prisms. However, band structure calculations on Y3Ru2Ge3 support an alternative description for RE 3 M 2Ge3 based on [M 2Ge3] layers built from linked MGe4 tetrahedra, which emphasizes the strong M–Ge covalent bonds present. The temperature dependence of the electrical resistivity of RE 3Ru2Ge3 generally indicates metallic behaviour but with low-temperature transitions visible for some members (RE=Gd, Tb, Dy) that are probably associated with magnetic ordering of the RE atoms. Anomalously, Y3Ru2Ge3 exhibits semiconductor-like behaviour of uncertain origin. Magnetic measurements on Dy3Ru2Ge3 reveal antiferromagnetic ordering at 3K and several unusual field-dependent transitions suggestive of complex spin reorientation processes. [ABSTRACT FROM AUTHOR]

Abstract: The ternary rare-earth zinc arsenides REZn2As3 (RE=La–Pr) have been prepared by reactions of the elements at 800°C. They adopt new tetragonal structure types, with the La member (space group I4/mmm, Z=4, a=4.1133(2)Å, c=32.1246(14)Å) differing from the Ce and Pr members (space group P4/nmm, Z=2, a=4.0804(6)–4.0534(12)Å, c=16.089(5)–16.059(10)Å, respectively) in the disposition of RE-centred square antiprisms on opposite sides of square As nets. The structures contain thick anionic slabs, built from edge-sharing ZnAs4 tetrahedra, that can be considered either as stackings of three PbO-type layers or as fragments of the fluorite-type structure. These slabs are deficient in Zn and are reminiscent of the same features in binary arsenide Zn3As2. LaZn2As3 exhibits temperature-independent paramagnetism whereas CeZn2As3 follows modified Curie–Weiss behavior consistent with Ce3+ species but with no occurrence of long-range ordering. [Copyright &y& Elsevier]

Abstract: The ternary arsenide BaAg2As2 has been prepared by reaction of the elements at 850°C. Single-crystal and powder X-ray diffraction analysis revealed that it adopts the ThCr2Si2-type structure (Pearson symbol tI10, space group I4/mmm, Z=2, a=4.6025(3)Å, c=10.8672(6)Å at 295K) featuring [Ag2As2] layers interconnected by homoatomic As–As bonds along the c-direction. Band structure calculations indicate no gap at the Fermi level, and support the occurrence of strong As–As and weak Ag–Ag bonding. The asymmetric lineshape and the absence of a BE shift in the Ag 3d5/2 core-line peak relative to the element suggest delocalization of the Ag valence electrons. A significant negative BE shift (1.0eV) in the As 3d5/2 core-line peak relative to the element confirms the presence of anionic As atoms. A reversible transition is observed at 175K in the electrical resistivity, and is probably related to a structural phase transition. [Copyright &y& Elsevier]

Abstract: Four ternary pnictides AAg4 Pn 2 (A=Sr, Eu; Pn=As, Sb) were prepared by reactions of the elements at 850°C and their crystal structures were determined from single-crystal X-ray diffraction studies. These silver-containing pnictides AAg4 Pn 2 adopt the trigonal CaCu4P2-type structure (Pearson symbol hR21, space group R3̄m, Z=3; a=4.5555(6)Å, c=24.041(3)Å for SrAg4As2; a=4.5352(2)Å, c=23.7221(11)Å for EuAg4As2; a=4.7404(4)Å, c=25.029(2)Å for SrAg4Sb2; a=4.7239(3)Å, c=24.689(2)Å for EuAg4Sb2), which can be derived from the trigonal CaAl2Si2-type structure of the isoelectronic zinc-containing pnictides AZn2 Pn 2 by insertion of additional Ag atoms into trigonal planar sites within [M 2 Pn 2]2− slabs built up of edge-sharing tetrahedra. Band structure calculations on SrAg4As2 and SrAg4Sb2 revealed that these charge-balanced Zintl phases actually exhibit no gap at the Fermi level and are predicted to be semimetals. [Copyright &y& Elsevier]

Abstract: The ternary rare-earth zinc arsenides REZn1−x As2 (RE=La–Nd, Sm) were prepared by reaction of the elements at 800°C. Single-crystal and powder X-ray diffraction analysis revealed a defect SrZnBi2-type average structure for the La member (Pearson symbol tI16, space group I4/mmm, Z=4; a=4.0770(9)Å, c=20.533(5)Å), in contrast to defect HfCuSi2-type average structures for the remaining RE members (Pearson symbol tP8, space group P4/nmm, Z=2; a=4.0298(5)–3.9520(4)Å, c=10.222(1)–10.099(1)Å in the progression from Ce to Sm). The homogeneity range is not appreciable (estimated to be narrower than 0.6<1−x<0.7 in SmZn1−x As2) and the formula REZn0.67As2 likely represents the Zn-rich phase boundary. The Ce–Nd members are Curie–Weiss paramagnets. LaZn0.67As2 shows activated behavior in its electrical resistivity, whereas SmZn0.67As2 exhibits anomalies in its temperature dependence of the electrical resistivity. [Copyright &y& Elsevier]

Abstract: The quaternary rare-earth phosphides RECuZnP2 (RE=Pr, Nd, Gd–Tm, Lu) have been prepared by reaction of the elements at 900°C, completing this versatile series which forms for nearly all RE metals. They adopt the trigonal CaAl2Si2-type structure (Pearson symbol hP5, space group P3̄m1, Z=1), as confirmed by single-crystal X-ray diffraction analysis on ErCuZnP2 and powder X-ray diffraction analysis on the remaining members. The Cu and Zn atoms are assumed to be disordered over the single transition-metal site. Band structure calculations on a hypothetically ordered YCuZnP2 model suggest a semimetal, with a zero band gap between the valence and conduction bands. This electronic structure is supported by XPS valence band spectra for RECuZnP2 (RE=Gd–Er), in which the intensity drops off smoothly at the Fermi edge. The absence of a band gap permits the electron count to deviate from the precise value of 16 e− per formula unit, as demonstrated by the formation of a solid solution in GdCu x Zn2−x P2 (1.0≤x≤1.3), while still retaining the CaAl2Si2-type structure. Because the Cu 2p XPS spectra indicate that the Cu atoms are always monovalent, the substitution of Cu for Zn leads to a decrease in electron count and a lowering of the Fermi level in the valence band. The magnetic susceptibility of RECuZnP2 (RE=Gd–Er), which obeys the Curie–Weiss law, confirms the presence of trivalent RE atoms. [ABSTRACT FROM AUTHOR]

Abstract: The ternary rare-earth-metal chromium gallides RE 4CrGa12 (RE=Tb–Tm) have been prepared by reactions of the elements at 1000°C in the presence of excess gallium used as a self-flux. Their structures are derived by inserting Cr atoms into a quarter of the empty Ga6 octahedral clusters found in the parent binary gallides REGa3 (AuCu3-type), although single-crystal X-ray diffraction studies suggest that complex superstructures may be adopted. An ideal ordered Y4PdGa12-type structure was successfully refined for a crystal of Dy4CrGa12 (Pearson symbol cI34, space group Im m, Z=2, a=8.572(1)Å). Magnetic measurements on single-crystal samples reveal ferromagnetic or possibly ferrimagnetic ordering for the Tb, Dy, and Er members (T C=22, 15, and 2.8K, respectively) and antiferromagnetic ordering for the Ho member (T N=7.5K). Band structure calculations on a hypothetical “Y4CrGa12” model suggest that the Cr atoms carry no local magnetic moment. [Copyright &y& Elsevier]

The novel I 4 -II-IV 2 -VI 7 quaternary diamond-like semiconductors (DLSs), Cu 4 ZnGe 2 S 7 and Cu 4 CdGe 2 S 7 , were prepared from the constituent elemental powders at elevated temperatures. Cu 4 ZnGe 2 S 7 crystallizes in the polar, chiral space group C 2 and adopts the Cu 4 NiSi 2 S 7 structure-type, which can be considered a derivative of the cubic diamond structure. The cadmium analog takes on the Cu 5 Si 2 S 7 structure-type, which is related to the hexagonal diamond structure, and displays polar, Cc space group symmetry. Both compounds contain [Ge 2 S 7 ]6- anions created by corner-sharing GeS 4 tetrahedra. The crystal structures were carefully evaluated using: 1) extended connectivity tables, 2) minimum bounding ellipsoid analysis, and 3) bond valence sum (BVS) and global instability index (G) calculations. Both compounds are thermally stable up to temperatures exceeding 950 °C and melt incongruently. As assessed using diffuse reflectance spectroscopy, Cu 4 ZnGe 2 S 7 and Cu 4 CdGe 2 S 7 possess optical bandgaps of 1.65 eV and 1.90 eV, respectively, which are narrower than the analogous I 2 -II-IV-VI 4 DLSs. Electronic structure calculations show that both compounds are direct-bandgap semiconductors with significant contributions of Cu- d and S- p orbitals to the states at the top of the valence band. While Cu 4 CdGe 2 S 7 displays a weak second harmonic generation (SHG) response, the second-order nonlinear optical susceptibility, χ(2), of Cu 4 ZnGe 2 S 7 is 14.8 ± 1.5 pm V-1, assessed using the Kurtz-Perry powder method and an optical-grade AgGaSe 2 (AGSe) reference. Both compounds exhibit laser-induced damage threshold values similar to AGSe, ∼0.1 GW cm-2, for λ = 1.064 µm using picosecond laser pulses. Most importantly, Cu 4 ZnGe 2 S 7 exhibits a phase-matching behavior at λ = 3.1 µm. These results suggest that Cu 4 ZnGe 2 S 7 holds potential for use in low-powered laser applications involving efficient wave mixing in the mid-IR region. [Display omitted] • Cu 4 ZnGe 2 S 7 is a novel diamond-like material with the Cu 4 NiSi 2 S 7 structure type. • Cu 4 CdGe 2 S 7 is a novel diamond-like material with the Cu 5 Si 2 S 7 structure type. • Optical bandgaps of Cu 4 ZnGe 2 S 7 and Cu 4 CdGe 2 S 7 are 1.65 and 1.90 eV, respectively. • Cu 4 ZnGe 2 S 7 has χ (2) value of 14.8 ± 1.5 pm V− 1 and is phase matching for λ = 3.1 µm. • Cu 4 ZnGe 2 S 7 is a candidate for low-powered laser applications in the mid-IR region. [ABSTRACT FROM AUTHOR]