Yb Substitution and Ultralow Thermal Conductivity of the Ca3-xYbxAlSb3 (0 ≤ x ≤ 0.81(1)) System

A series of Yb-substituted Zintl phases in the Ca_3-xYb_xAlSb₃ (0 ≤ x ≤ 0.81(1)) system has been synthesized by initial arc melting and post-heat treatment, and their isotypic crystal structures were characterized by both powder and single crystal X-ray diffraction analysis. All four title compounds adopted the Ca₃AlAs₃-type structure (space group Pnma, Pearson code oP28, Z = 4). The overall structure can be described as a combination of the 1-dimensional (1D) infinite chain of _∞¹[Al(Sb₂Sb_2/2)] formed by two vertices sharing [AlSb₄] tetrahedral moieties and three Ca²⁺/Yb²⁺ mixed sites located in between these 1D chains. The charge balance and the resultant independency of the 1D chains in the title system were explained by the Zintl-Klemm formalism [Ca²⁺/Yb²⁺]₃[(4b-Al^1-)(1b-Sb^2-)₂(2b-Sb^1-)_2/2]. A series of DFT calculations proved that (1) the band overlap between the d-orbital states from two types of cations and the p-orbital states from Sb at the high symmetry Γ point implied a heavily doped degenerate semiconducting behavior of the quaternary Ca₂YbAlSb₃ model and (2) the site preference of Yb for the M1 site was due to the electronic-factor criterion based on the Q values of each atomic site. The electron localization function calculations also proved that the two different shapes of lone pairs of the Sb atoms─the "umbrella-shape" and the "C-shape"─are determined by local geometry and the coordination environment on the anionic frameworks. Thermoelectric measurements of the quaternary title compound Ca_2.19(1)Yb_0.81AlSb₃ showed an approximately two times larger ZT value than that of ternary Ca₃AlSb₃ at 623 K due to increased electrical conductivity and ultralow thermal conductivity originated from Yb substitution for Ca.

Experimental and Theoretical Study on the Nonmagnetic Li/Mg Cosubstitution in the Gd5-x(Li/Mg)xGe4 (x = 1.04, 1.17, 1.53) System

Three Li- and Mg-cosubstituted compounds in the Gd_5-x(Li/Mg)_xGe₄ (x = 1.04(2), 1.17(2), 1.53(2)) system have been successfully prepared by conventional high-temperature reactions. According to powder and single-crystal X-ray diffraction analyses, all three compounds adopt a Gd₅Si₄-type phase with the orthorhombic Pnma space group (Pearson code oP16, Z = 4) and six crystallographically independent atomic sites. The crystal structure can be described as a combination of two-dimensional Mo₂FeB₂-type _∞²[Gd₂(Li/Mg)Ge₂] layers and [Ge₂] dimers. Interestingly, as 64% of Li and 26% of Gd at the RE3 and RE2 sites, respectively, were exclusively substituted by Mg in Gd_3.47(1)Li_0.36(2)Mg_1.17(3)Ge₄, the lattice parameter b was selectively shortened as a result of the RE3-Ge1 bond shrinkage in comparison to that in Gd₄LiGe₄, while lattice parameters a and c remained nearly intact. A series of theoretical calculations using the tight-binding linear muffin-tin orbital (TB-LMTO) method indicated that the reduction of the particular RE3-Ge1 bond distance in the title compounds could also be explained by an optimization of bonding based on the corresponding RE3-Ge1 crystal orbital Hamilton population (COHP) curve. Moreover, the specific site preference of Mg for the RE3 site was supported by both size-factor as well as electronic-factor criteria on the basis of the smallest atomic size and the highest electronegativity of Mg among the three cations. Therefore, the overall electronic structure was further interrogated by a density of states (DOS) analysis. The influence of nonmagnetic Li/Mg cosubstitution for the magnetic Gd atoms in the title Gd_5-x(Li/Mg)_xGe₄ system on the magnetic characteristics was also thoroughly studied by isofield magnetization at 100 Oe and 10 kOe and isothermal magnetization measurements at 4 K using two of the title compounds: Gd_3.83(1)Li_0.48Mg_0.69(3)Ge₄ and Gd_3.47(1)Li_0.36(2)Mg_1.17(3)Ge₄.

p-Type Double Doping and the Diamond-like Morphology Shift of the Zintl Phase Thermoelectric Materials: The Ca11-xAxSb10-yGez (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) System

Five ternary and quaternary Zintl phases in the solid-solution Ca_11-xA_xSb_10-yGe_z (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) system have been successfully synthesized by both of the arc-melting and the molten Pb metal-flux reactions. The crystal structure of these title compounds was characterized by powder and single-crystal X-ray diffractions analyses, and all title compounds crystallized in the Ho₁₁Ge₁₀-type phase in the tetragonal space group I4/mmm (Z = 4, Pearson code tI84). The complex crystal structure can be described as an assembly of 1) three kinds of cationic polyhedra centered by three different Sb and 2) the cage-shaped anionic frameworks built through the connection of two types of Sb. The newly substituted p-type double dopants of the cationic (Na and Li) and anionic (Ge) elements displayed particular site preferences, which were successfully explained by either the size-factor criterion based on the atomic size or the electronic-factor criterion based on the electronegativity of an element. Quite interestingly, as the reaction conditions were changed, the morphology shift of single crystals in Ca_10.94(3)Na_0.06Sb_9.58(1)Ge_0.21 occurred from a cubic-shaped to a hummocky-type, to a hopper-type, and eventually to an octahedral-shaped crystal, just like the Yakutian kimberlite diamonds. Moreover, we firmly believe that the inclusion of the p-type Ge dopant for Sb was crucial to trigger this type of morphology shift and complete the octahedral-shaped morphology in the overall crystal-growth mechanism. The theoretical calculations using a DFT method rationalized the observed site preference of Na and the electronic effect of the p-type Ge dopants. The Seebeck coefficient measurements for Ca_10.88(4)Li_0.12Sb_9.45(1)Ge_0.21 indicated that some portions of electron charge carriers were effectively eliminated by the p-type double dopants using Li and Ge.

Early stage of the single-crystal growth and tipping point of the cationic site preference in Gd-doped Zintl phase thermoelectric materials

Three novel Zintl phases in the Ca11−xGdxSb10−y system were synthesized, and the early stage of the single-crystal growth process and the “tipping point” of the cationic site preference for the size-factor criterion were thoroughly investigated.

Two Steps to Improve the Thermoelectric Performance of the Ca5-xYbxAl2-yInySb6 System

A series of quaternary and quinary Zintl phase thermoelectric (TE) compounds, Ca_5-xYb_xAl_2-yIn_ySb₆ (3.07(1) ≤ x ≤ 4.88(2); 0.16(2) ≤ y ≤ 2.00), containing Al/In mixed sites as well as Ca/Yb mixed sites has been successfully synthesized by a direct arc-melting method, and the X-ray diffraction analyses indicated that the products initially adopted an orthorhombic Ba₅Al₂Bi₆-type structure (space group Pbam, Z = 2). However, after a postannealing process at 973 K for 1 month, the particular Yb rich compounds underwent a transformation of the original structure type to a Ca₅Ga₂Sb₆-type phase regardless of the In substitution for Al. The noticeable site preference of cationic Ca and Yb in the three available cationic sites could be understood on the basis of a size match between the central cation and the volume of the anionic polyhedra. The observed phase transition was nicely explained by DFT calculations, proving that the Ca₅Ga₂Sb₆-type phase was energetically more favorable than the Ba₅Al₂Sb₆-type phase for the particular Yb-rich compound. Moreover, this energy difference between the two title phases was originally the result of both the site energy in the Ca site and the bond energies in the [(Al/In)₂Sb₈] anionic building blocks. A series of thermoelectric property data indicated that a two-step process involving a partial/full In substitution for Al and a phase transition from the Ba₅Al₂Sb₆-type to the Ca₅Ga₂Sb₆-type phase successfully enhanced the electrical conductivities and the Seebeck coefficients of the title compounds. This kind of combined effect eventually resulted in a ZT improvement for the quinary compound Ca_1.14(2)Yb_3.86Al_1.68(1)In_0.32Sb₆ by approximately 4 times in comparison to its quaternary predecessor Ca_1.55(1)Yb_3.45Al₂Sb₆.

Anionic Doping and Cationic Site Preference in CaYb4Al2Sb6- xGe x ( x = 0.2, 0.5, 0.7): Origin of the Enhanced Seebeck Coefficient and the Structural Transformation

Three Zintl phase compounds belonging to the CaYb₄Al₂Sb_{6- x}Ge _x ( x = 0.2, 0.5, 0.7; nominal compositions) system with various Ge-doping contents were successfully synthesized by arc-melting and were initially crystallized in the Ba₅Al₂Bi₆-type phase (space group Pbam, Pearson codes oP26). However, after post-heat treatment at an elevated temperature, the originally obtained crystal structure was transformed into the homeotypic Ca₅Ga₂Sb₆-type structure according to powder and single-crystal X-ray diffraction analyses. Two types of crystal structures share some isotypic structural moieties, such as the one-dimensional anionic chains formed by _∞¹[Al₂Sb₈] and the void-filling Ca²⁺/Yb²⁺ mixed cations, but the slightly different spatial arrangements in each unit cell make these two structural types distinguishable. This series of title compounds is originally investigated to examine whether anionic p-type doping using Ge can successfully enhance thermoelectric (TE) properties of the Yb-rich CaYb₄Al₂Sb_{6- x}Ge _x series even after the phase transition from the Ba₅Al₂Bi₆-type to the Ca₅Ga₂Sb₆-type phase. More interestingly, we also reveal that the given structural transformation is triggered by the particularly different site-preference of Ca²⁺ and Yb²⁺ among three available cationic sites in each structure type, which is significantly affected by thermodynamic conditions of this system. Band structure and density of states analyses calculated by density functional theory using the tight-binding linear muffin-tin orbital method also prove that the Ge-doping actually increases band degeneracies and the number of resonant peaks near the Fermi level resulting in the improvement of Seebeck coefficients. Electron localization function analyses for the (0 1 0) sliced-plane and the 3D isosurface nicely illustrates the distortion of the paired-electron densities due to the introduction of Ge. The systematic TE property measurements imply that the attempted anionic p-type doping is indeed effective to improve the TE characteristics of the title CaYb₄Al₂Sb_{6- y}Ge _y system.

Cs3VO(O2)2CO3: an exceptionally thermostable carbonatoperoxovanadate with an extremely large second-harmonic generation response

A highly thermostable carbonatoperoxovanadate, Cs₃VO(O₂)₂CO₃, exhibits a remarkably strong SHG response of approximately 23.0 times that of KDP, which is the largest among those of the reported NLO carbonate materials.

A novel nonlinear optical (NLO) carbonatoperoxovanadate, Cs₃VO(O₂)₂CO₃, with an exceptionally high thermostability was successfully synthesized by introducing highly polarizable Cs⁺ cations and inorganic polydentate carbonate anions into asymmetric peroxovanadates. The structure of Cs₃VO(O₂)₂CO₃ is composed of distorted [VO(O₂)₂CO₃]^3– units and charge balancing Cs⁺ cations. The title compound exhibits the largest NLO intensity ever found in the current carbonate NLO materials, i.e., 23.0 times that of KH₂PO₄ (KDP). The remarkably strong second-harmonic generation (SHG) response originates from the synergistic effect of the exceedingly polarizable Cs⁺ cations, distortive polyhedra of the V⁵⁺ cation, delocalized π orbitals in CO₃ groups, and distorted localized π orbitals in O₂ groups. First-principles calculations indicated that introducing the polarizable cations into peroxovanadates not only induces the enhancement of the SHG response but also improves the thermal stability of the framework.

Structure and Chemical Bonding of the Li-Doped Polar Intermetallic RE₂In1-xLixGe₂ (RE = La, Nd, Sm, Gd; x = 0.13, 0.28, 0.43, 0.53) System

Four polar intermetallic compounds belonging to the RE₂In_1-xLi_xGe₂ (RE = La, Nd, Sm, Gd; x = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system have been synthesized by the traditional solid-state reaction method, and their crystal structures have been characterized by single-crystal X-ray diffraction (SXRD) analyses. The isotypic crystal structures of four title compounds adopt the Mo₂FeB₂-type structure having the tetragonal space group P4/mbm (Z = 2, Pearson code tP40) with three crystallographically independent atomic sites and can be simply described as a pile of the identical 2-dimensioanl (2D) RE₂In_1-xLi_xGe₂ slabs stacked along the c-axis direction. The substituting Li atom shows a particular site preference for replacing In at the Wyckoff 2a site rather than Ge at the Wyckoff 4g in this crystal structure. As the size of a used rare-earth metal decreases from La³⁺ to Gd³⁺ throughout the title system, the Ge-Ge and Ge-In/Li bond distances, both of which consist of the 2D anionic Ge₂(In/Li) layer, gradually decrease resulting in the reduction of a unit cell volume. A series of theoretical investigations has been performed using a hypothetical structure model Gd₂In_0.5Li_0.5Ge₂ by tight-binding linear muffin-tin orbital (TB-LMTO) method. The resultant densities of states (DOS) value at the Fermi level (E_F) suggests a metallic conductivity for this particular composition, and this calculation result is in a good agreement with the formal charge distribution assigning two extra valence electrons for a metal-metal bond in the conduction band. The thorough analyses of six crystal orbital Hamilton population (COHP) curves representing various interatomic interactions and an electron localization function (ELF) diagram indicating the locations of paired-electron densities are also provided in this article.

Single and double-doping effects on the thermoelectric properties of two Zintl compounds: Eu11Bi8.07(2)Sn1.93 and Eu10.74(2)K0.26Bi9.14(2)Sn0.86

Two Zintl phase thermoelectric compounds of Eu_11-xK_xBi_10-ySn_y (x = 0, 0.26(1); y = 0.86(2), 1.93(2)) have been synthesized by a high-temperature solid-state reaction and arc-melting methods. The two isotypic crystal structures are characterized by both single-crystal and powder X-ray diffractions, and adopt a tetragonal Ho₁₁Ge₁₀-type structure (space group I4/mmm, Z = 2, Pearson code tI84) containing nine crystallographically independent asymmetric atomic sites in a unit cell. The chemical compositions are confirmed by EDS analysis. The complex crystal structure of the two title compounds can be described as an assembly of three different types of co-facial polyhedra formed by cations and 3-dimensional anionic frameworks surrounding these polyhedra. A quaternary title compound, Eu_10.74(2)K_0.26Bi_9.14(2)Sn_10.86, which simultaneously contains both cationic and anionic p-dopants in a single compound, was successfully crystallized for the first time in the A₁₁M₁₀ (A = alkaline-earth metals, rare-earth metals; M = triels, tetrels, pnictogens) series. In particular, two different types of p-dopants K and Sn show particular site-preferences, respectively, where K and Sn prefer to occupy the cationic Wyckoff 4e site and the anionic Wyckoff 8h site. These noticeable site preferences can be elucidated by either a size-factor criterion for the K-doping case or by an electronic-factor criterion for the Sn-doping case. The tight-binding linear muffin-tin orbital calculations show that as the double p-doping is applied to the Eu_11-xK_xBi_10-ySn_y system, some extra holes are generated on the electronic structures according to the density of states curves. However, a series of thermoelectric property measurements prove that this extra hole-carrier doping is hardly effective enough to completely suppress a bipolar conduction of holes and electrons due to the rigid metallic band structure of the title system.

Effect of MultiSubstitution on the Thermoelectric Performance of the Ca11-xYbxSb10-yGez (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) System: Experimental and Theoretical Studies

The Zintl phase solid-solution Ca_11-xYb_xSb_10-yGe_z (0 ≤ x ≤ 9; 0 ≤ y ≤ 3; 0 ≤ z ≤ 3) system with the cationic/anionic multisubstitution has been synthesized by molten Sn metal flux and arc-melting methods. The crystal structure of the nine title compounds were characterized by both powder and single-crystal X-ray diffractions and adopted the Ho₁₁Ge₁₀-type structure with the tetragonal space group I4/mmm (Z = 4, Pearson Code tI84). The overall isotypic structure of the nine title compounds can be illustrated as an assembly of three different types of cationic polyhedra sharing faces with their neighboring polyhedra and the three-dimensional cage-shaped anionic frameworks consisting of the dumbbell-shaped Sb₂ units and the square-shaped Sb₄ or (Sb/Ge)₄ units. During the multisubstitution trials, interestingly, we observed a metal-to-semiconductor transition as the Ca and Ge contents increased in the title system from Yb₁₁Sb₁₀ to Ca₉Yb₂Sb₇Ge₃ (nominal compositions) on the basis of a series of thermoelectric property measurements. This phenomenon can be elucidated by the suppression of a bipolar conduction of holes and electrons via an extra hole-carrier doping. The tight-binding linear muffin-tin orbital calculations using four hypothetical structural models nicely proved that the size of a pseudogap and the magnitude of the density of states at the Fermi level are significantly influenced by substituting elements as well as their atomic sites in a unit cell. The observed particular cationic/anionic site preferences, the historically known abnormalities of atomic displacement parameters, and the occupation deficiencies of particular atomic sites are further rationalized by the QVAL value criterion on the basis of the theoretical calculations. The results of SEM, EDS, and TGA analyses are also provided.

Cationic Site-Preference in the Yb14-xCaxAlSb11 (4.81 ≤ x ≤ 10.57) Series: Theoretical and Experimental Studies

Four quaternary Zintl phases with mixed-cations in the Yb_14-xCa_xAlSb₁₁ (4.81 ≤ x ≤ 10.57) series have been synthesized by using the arc-melting and the Sn metal-flux reaction methods, and the isotypic crystal structures of the title compounds have been characterized by both powder and single-crystal X-ray diffraction (PXRD and SXRD) analyses. The overall crystal structure adopting the Ca₁₄AlSb₁₁-type can be described as a pack of four different types of the spiral-shaped one-dimensional octahedra chains with various turning radii, each of which is formed by the distorted ((Yb/Ca)Sb₆) octahedra. Four symmetrically-independent cationic sites contain mixed occupations of Yb²⁺ and Ca²⁺ with different mixing ratios and display a particular site preference by two cationic elements. Two hypothetical structural models of Yb₄Ca₁₀AlSb₁₁ with different cationic arrangements were designed and exploited to study the details of site and bond energies. QVAL values provided the rationale for the observed site preference based on the electronegativity of each atom. Density of states (DOS) curves indicated a semiconducting property of the title compounds, and crystal orbital Hamilton population (COHP) plots explained individual chemical bonding between components. Thermal conductivity measurement was performed for Yb_8.42(4)Ca_5.58AlSb₁₁, and the result was compared to compounds without mixed cations.

ACdCO3F (A = K and Rb): new noncentrosymmetric materials with remarkably strong second-harmonic generation (SHG) responses enhanced via π-interaction

The remarkably large SHG efficiency of KCdCO₃F originates from enhancement via interatomic interactions between the s and p states of Cd²⁺ and the π-conjugated groups of the [CO₃]²⁻ unit.

Lead sulfide nanocrystal quantum dot solar cells with trenched ZnO fabricated via nanoimprinting

The improvement of power conversion efficiency, especially current density (Jsc), for nanocrystal quantum dot based heterojunction solar cells was realized by employing a trenched ZnO film fabricated using nanoimprint techniques. For an optimization of ZnO patterns, various patterned ZnO films were investigated using electrical and optical analysis methods by varying the line width, interpattern distance, pattern height, and residual layer. Analyzing the features of patterned ZnO films allowed us to simultaneously optimize both the pronounced electrical effects as well as optical properties. Consequently, we achieved an enhancement in Jsc from 7.82 to 12.5 mA cm(-2) by adopting the patterned ZnO with optimized trenched shape.

Synthesis, crystal structures and chemical bonding of RE5−xLixGe4(RE = Nd, Sm and Gd;x≃ 1) with the orthorhombic Gd5Si4type

The syntheses and single-crystal and electronic structures of three new ternary lithium rare earth germanides, RE5−xLixGe4(RE = Nd, Sm and Gd;x≃ 1), namely tetrasamarium lithium tetragermanide (Sm3.97Li1.03Ge4), tetraneodymium lithium tetragermanide (Nd3.97Li1.03Ge4) and tetragadolinium lithium tetragermanide (Gd3.96Li1.03Ge4), are reported. All three compounds crystallize in the orthorhombic space groupPnmaand adopt the Gd5Si4structure type (Pearson codeoP36). There are six atoms in the asymmetric unit: Li1 in Wyckoff site 4c, RE1 in 8d, RE2 in 8d, Ge1 in 8d, Ge2 in 4cand Ge3 in 4c. One of the RE sites,i.e.RE2, is statistically occupied by RE and Li atoms, accounting for the small deviation from ideal RE4LiGe4stoichiometry.

Synthesis, crystal chemistry, and magnetic properties of RE7Li8Ge10 and RE11Li12Ge16 (RE = La-Nd, Sm): new members of the [REGe2](n)[RELi2Ge](m) homologous series

Eight new rare-earth metal-lithium-germanides belonging to the [REGe(2)](n)[RELi(2)Ge](m) homologous series have been synthesized and structurally characterized by single-crystal X-ray diffraction. The structures of the title compounds can be rationalized as linear intergrowths of imaginary RELi(2)Ge (MgAl(2)Cu structure type) and REGe(2) (AlB(2) structure type) slabs. The compounds with general formula RE(7)Li(8)Ge(10) (RE = La-Nd, Sm), i.e., [REGe(2)](3)[RELi(2)Ge](4), crystallize in the orthorhombic space group Cmmm (No. 65) with a new structure type. Similarly, the compounds with general formula RE(11)Li(12)Ge(16) (RE = Ce-Nd), i.e., [REGe(2)](5)[RELi(2)Ge](6), crystallize in the orthorhombic space group Immm (No. 71) also with its own structure type. Temperature-dependent DC magnetization measurements indicate Curie-Weiss paramagnetism in the high-temperature regime and hint at complex magnetic ordering at low temperatures. The measured effective moments are consistent with RE(3+) ground states in all cases. The experimental results have been complemented by tight-binding linear muffin-tin orbital (TB-LMTO) electronic structure calculations.

Diytterbium(II) lithium indium(III) digermanide, Yb(2)LiInGe(2)

The title compound, Yb₂LiInGe₂, a new ordered quaternary inter­metallic phase, crystallizes with the ortho­rhom­bic Ca₂LiInGe₂ type (Pearson code oP24). The crystal structure contains six crystallographically unique sites in the asymmetric unit, all in special positions with site symmetry .m.. The structure is complex and based on [InGe₄] tetra­hedra, which share corners in two directions, forming layers parallel to (001). Yb atoms fill square-pyramidal (Yb1) and octa­hedral (Yb2) inter­stices between the [InGe_4/2] layers, while the small Li⁺ atoms fill tetra­hedral sites.

Planar versus Puckered Nets in the Polar Intermetallic Series EuGaTt (Tt = Si, Ge, Sn)

The ternary polar intermetallic compounds EuGaTt (Tt = Si, Ge, Sn) have been synthesized and characterized experimentally, as well as theoretically. EuGaSi crystallizes in the hexagonal AlB(2)-type structure (space group P6/mmm, Z = 1, Pearson symbol hP3) with randomly distributed Ga and Si atoms on the graphite-type planes: a = 4.1687(6) A, c = 4.5543(9) A. On the other hand, EuGaGe and EuGaSn adopt the hexagonal YPtAs-type structure (space group P6(3)/mmc, Z = 4, Pearson symbol hP12): a = 4.2646(6) A and c = 18.041(5) A for EuGaGe; a = 4.5243(5) A and c = 18.067(3) A for EuGaSn. The three crystal structures contain formally [GaTt](2-) polyanionic 3-bonded, hexagonal networks, which change from planar to puckered and exhibit a significant decrease in interlayer Ga-Ga distances as the size of Tt increases. Magnetic susceptibility measurements of this series of compounds show Curie-Weiss behavior above 86(5), 95(5), and 116(5) K with magnetic moments of 7.93, 7.97, and 7.99 mu(B) for EuGaSi, EuGaGe, and EuGaSn, respectively, indicating a 4f(7) electronic configuration (Eu(2+)) for Eu atoms. X-ray absorption spectra (XAS) are also consistent with these magnetic properties. Electronic structure calculations supplemented by a crystal orbital Hamilton population (COHP) analysis identifies the synergy between atomic sizes, from both Eu and Tt atoms, and the orbital contributions from Eu toward influencing the structural features of EuGaTt. A multicentered interaction between planes of Eu atoms and the [GaTt](2-) layers rather than through-space Ga-Ga bonding is seen in ELF distributions.