Editorial

3 pages, 149 KiB

Open AccessEditorial

by Susan M. Kauzlarich

Materials 2019, 12(16), 2554; https://doi.org/10.3390/ma12162554 - 11 Aug 2019

Cited by 20 | Viewed by 2709

Zintl phases have garnered a great deal of attention for many applications. The term “Zintl phase” recognizes the contributions of the German chemist Eduard Zintl to the field of solid-state chemistry. While Zintl phases were initially defined as a subgroup of intermetallic phases [...] Read more.

Zintl phases have garnered a great deal of attention for many applications. The term “Zintl phase” recognizes the contributions of the German chemist Eduard Zintl to the field of solid-state chemistry. While Zintl phases were initially defined as a subgroup of intermetallic phases where cations and anions or polyanions in complex intermetallic structures are valence satisfied, the foundational idea of electron counting to understand complex solid-state structures has provided insight into bonding and a bridge between solid-state and molecular chemists. This Special Issue, “Advances in Zintl Phases”, provides a collage of research in the area, from solution to solid-state chemistry. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

Research

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10 pages, 1871 KiB

Open AccessArticle

Synthesis of the Tetragonal Phase of Zintl’s NaTl and Its Structure Determination from Powder Diffraction Data

by Susanne Tiefenthaler, Nikolaus Korber and Stefanie Gärtner

Materials 2019, 12(8), 1356; https://doi.org/10.3390/ma12081356 - 25 Apr 2019

Cited by 6 | Viewed by 2797

Abstract

A tetragonal distortion of the long-time known NaTl structure at 298 K was observed in different experimental setups, including Zintl’s original procedure of reducing Tl(I)-iodide by sodium liquid ammonia solutions. The powder diffraction pattern obtained by the high temperature synthesis using classical solid-state [...] Read more.

A tetragonal distortion of the long-time known NaTl structure at 298 K was observed in different experimental setups, including Zintl’s original procedure of reducing Tl(I)-iodide by sodium liquid ammonia solutions. The powder diffraction pattern obtained by the high temperature synthesis using classical solid-state techniques allowed a model-independent unambiguous structure solution and refinement of tetragonal distorted NaTl (Rp = 0.0179, wRp = 0.0246, R = 0.0477, wR = 0.0527, GooF = 1.24). Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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9 pages, 1552 KiB

Open AccessFeature PaperArticle

Thermoelectric Properties of Scandium Sesquitelluride

by Dean Cheikh, Kathleen Lee, Wanyue Peng, Alexandra Zevalkink, Jean-Pierre Fleurial and Sabah K. Bux

Materials 2019, 12(5), 734; https://doi.org/10.3390/ma12050734 - 04 Mar 2019

Cited by 14 | Viewed by 3095

Abstract

Rare-earth (RE) tellurides have been studied extensively for use in high-temperature thermoelectric applications. Specifically, lanthanum and praseodymium-based compounds with the Th₃P₄ structure type have demonstrated dimensionless thermoelectric figures of merit (zT) up to 1.7 at 1200 K. Scandium, [...] Read more.

Rare-earth (RE) tellurides have been studied extensively for use in high-temperature thermoelectric applications. Specifically, lanthanum and praseodymium-based compounds with the Th₃P₄ structure type have demonstrated dimensionless thermoelectric figures of merit (zT) up to 1.7 at 1200 K. Scandium, while not part of the lanthanide series, is considered a RE element due to its chemical similarity. However, little is known about the thermoelectric properties of the tellurides of scandium. Here, we synthesized scandium sesquitelluride (Sc₂Te₃) using a mechanochemical approach and formed sintered compacts through spark plasma sintering (SPS). Temperature-dependent thermoelectric properties were measured from 300–1100 K. Sc₂Te₃ exhibited a peak zT = 0.3 over the broad range of 500–750 K due to an appreciable power factor and low-lattice thermal conductivity in the mid-temperature range. Full article

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12 pages, 3771 KiB

Open AccessFeature PaperArticle

Seebeck and Figure of Merit Enhancement by Rare Earth Doping in Yb_14-xRE_xZnSb₁₁ (x = 0.5)

by Elizabeth L. Kunz Wille, Navtej S. Grewal, Sabah K. Bux and Susan M. Kauzlarich

Materials 2019, 12(5), 731; https://doi.org/10.3390/ma12050731 - 03 Mar 2019

Cited by 20 | Viewed by 4337

Abstract

Yb₁₄ZnSb₁₁ has been of interest for its intermediate valency and possible Kondo designation. It is one of the few transition metal compounds of the Ca₁₄AlSb₁₁ structure type that show metallic behavior. While the solid solution of Yb [...] Read more.

Yb₁₄ZnSb₁₁ has been of interest for its intermediate valency and possible Kondo designation. It is one of the few transition metal compounds of the Ca₁₄AlSb₁₁ structure type that show metallic behavior. While the solid solution of Yb₁₄Mn_1-xZn_xSb₁₁ shows an improvement in the high temperature figure of merit of about 10% over Yb₁₄MnSb₁₁, there has been no investigation of optimization of the Zn containing phase. In an effort to expand the possible high temperature p-type thermoelectric materials with this structure type, the rare earth (RE) containing solid solution Yb_14-xRE_xZnSb₁₁ (RE = Y, La) was investigated. The substitution of a small amount of 3+ rare earth (RE) for Yb²⁺ was employed as a means of optimizing Yb₁₄MnSb₁₁ for use as a thermoelectric material. Yb₁₄ZnSb₁₁ is considered an intermediate valence Kondo system where some percentage of the Yb is formally 3+ and undergoes a reduction to 2+ at ~85 K. The substitution of a 3+ RE element could either replace the Yb³⁺ or add to the total amount of 3+ RE and provides changes to the electronic states. RE = Y, La were chosen as they represent the two extremes in size as substitutions for Yb: a similar and much larger size RE, respectively, compared with Yb³⁺. The composition x = 0.5 was chosen as that is the typical amount of RE element that can be substituted into Yb₁₄MnSb₁₁. These two new RE containing compositions show a significant improvement in Seebeck while decreasing thermal conductivity. The addition of RE increases the melting point of Yb₁₄ZnSb₁₁ so that the transport data from 300 K to 1275 K can be collected. The figure of merit is increased five times over that of Yb₁₄ZnSb₁₁ and provides a zT ~0.7 at 1275 K. Full article

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8 pages, 727 KiB

Open AccessArticle

Limits of Cation Solubility in AMg₂Sb₂ (A = Mg, Ca, Sr, Ba) Alloys

by Wanyue Peng and Alexandra Zevalkink

Materials 2019, 12(4), 586; https://doi.org/10.3390/ma12040586 - 15 Feb 2019

Cited by 7 | Viewed by 3255

Abstract

A M_{2} X_{2}

compounds that crystallize in the CaAl

_{2}

Si

_{2}

structure type have emerged as a promising class of n- and p-type thermoelectric materials. Alloying on the cation (A) site is a frequently used approach [...] Read more.

A M_{2} X_{2}

compounds that crystallize in the CaAl

_{2}

Si

_{2}

structure type have emerged as a promising class of n- and p-type thermoelectric materials. Alloying on the cation (A) site is a frequently used approach to optimize the thermoelectric transport properties of

A M_{2} X_{2}

compounds, and complete solid solubility has been reported for many combinations of cations. In the present study, we investigate the phase stability of the AMg

_{2}

Sb

_{2}

system with mixed occupancy of Mg, Ca, Sr, or Ba on the cation (A) site. We show that the small ionic radius of Mg

^{2 +}

leads to limited solubility when alloyed with larger cations such as Sr or Ba. Phase separation observed in such cases indicates a eutectic-like phase diagram. By combining these results with prior alloying studies, we establish an upper limit for cation radius mismatch in

A M_{2} X_{2}

alloys to provide general guidance for future alloying and doping studies. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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10 pages, 15666 KiB

Open AccessArticle

Synthesis and Characterization of K and Eu Binary Phosphides

by Juli-Anna Dolyniuk, Justin Mark, Shannon Lee, Nhon Tran and Kirill Kovnir

Materials 2019, 12(2), 251; https://doi.org/10.3390/ma12020251 - 13 Jan 2019

Cited by 4 | Viewed by 3507

Abstract

The synthesis, structural characterization, and optical properties of the binary Zintl phases of α-EuP₃, β-EuP₃, EuP₂, and α-K₄P₆ are reported in this study. These crystal structures demonstrate the versatility of P [...] Read more.

The synthesis, structural characterization, and optical properties of the binary Zintl phases of α-EuP₃, β-EuP₃, EuP₂, and α-K₄P₆ are reported in this study. These crystal structures demonstrate the versatility of P fragments with dimensionality varying from 0D (P₆ rings in α-K₄P₆) to 1D chains (EuP₂) to 2D layers (both EuP₃). EuP₂ is isostructural to previously reported SrP₂ and BaP₂ compounds. The thermal stabilities of the EuP₂ and both EuP₃ phases were determined using differential scanning calorimetry (DSC), with melting temperatures of 1086 K for the diphosphide and 1143 K for the triphosphides. Diffuse reflectance spectroscopy indicated that EuP₂ is an indirect semiconductor with a direct bandgap of 1.12(5) eV and a smaller indirect one, less than 1 eV. Both EuP₃ compounds had bandgaps smaller than 1 eV. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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13 pages, 4225 KiB

Open AccessArticle

High-Pressure Synthesis and Chemical Bonding of Barium Trisilicide BaSi₃

by Julia-Maria Hübner, Lev Akselrud, Walter Schnelle, Ulrich Burkhardt, Matej Bobnar, Yurii Prots, Yuri Grin and Ulrich Schwarz

Materials 2019, 12(1), 145; https://doi.org/10.3390/ma12010145 - 04 Jan 2019

Cited by 8 | Viewed by 3575

Abstract

BaSi₃ is obtained at pressures between 12(2) and 15(2) GPa and temperatures from 800(80) and 1050(105) K applied for one to five hours before quenching. The new trisilicide crystallizes in the space group I

\bar{4}

2m (no. 121) and adopts a [...] Read more.

BaSi₃ is obtained at pressures between 12(2) and 15(2) GPa and temperatures from 800(80) and 1050(105) K applied for one to five hours before quenching. The new trisilicide crystallizes in the space group I

\bar{4}

2m (no. 121) and adopts a unique atomic arrangement which is a distorted variant of the CaGe₃ type. At ambient pressure and 570(5) K, the compound decomposes in an exothermal reaction into (hP3)BaSi₂ and two amorphous silicon-rich phases. Chemical bonding analysis reveals covalent bonding in the silicon partial structure and polar multicenter interactions between the silicon layers and the barium atoms. The temperature dependence of electrical resistivity and magnetic susceptibility measurements indicate metallic behavior. Full article

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14 pages, 2635 KiB

Open AccessArticle

Thermal Stability and Thermoelectric Properties of NaZnSb

by Volodymyr Gvozdetskyi, Bryan Owens-Baird, Sangki Hong and Julia V. Zaikina

Materials 2019, 12(1), 48; https://doi.org/10.3390/ma12010048 - 24 Dec 2018

Cited by 17 | Viewed by 4265

Abstract

A layered Zintl antimonide NaZnSb (PbClF or Cu₂Sb structure type; P4/nmm) was synthesized using the reactive sodium hydride NaH precursor. This method provides comprehensive compositional control and facilitates the fast preparation of high-purity samples in large quantities. NaZnSb [...] Read more.

A layered Zintl antimonide NaZnSb (PbClF or Cu₂Sb structure type; P4/nmm) was synthesized using the reactive sodium hydride NaH precursor. This method provides comprehensive compositional control and facilitates the fast preparation of high-purity samples in large quantities. NaZnSb is highly reactive to humidity/air and hydrolyzes to NaOH, ZnO, and Sb in aerobic conditions. On the other hand, NaZnSb is thermally stable up to 873 K in vacuum, as no structural changes were observed from high-temperature synchrotron powder X-ray diffraction data in the 300–873 K temperature range. The unit cell expansion upon heating is isotropic; however, interatomic distance elongation is not isotropic, consistent with the layered structure. Low- and high-temperature thermoelectric properties were measured on pellets densified by spark plasma sintering. The resistivity of NaZnSb ranges from 11 mΩ∙cm to 31 mΩ∙cm within the 2–676 K range, consistent with heavily doped semiconductor behavior, with a narrow band gap of 0.23 eV. NaZnSb has a large positive Seebeck coefficient (244 μV∙K⁻¹ at 476 K), leading to the maximum of zT of 0.23 at 675 K. The measured thermoelectric properties are in good agreement with those predicted by theoretical calculations. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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13 pages, 4244 KiB

Open AccessArticle

Exploratory Work in the Quaternary System of Ca–Eu–Cd–Sb: Synthesis, Crystal, and Electronic Structures of New Zintl Solid Solutions

by Alexander Ovchinnikov, Gregory M. Darone, Bayrammurad Saparov and Svilen Bobev

Materials 2018, 11(11), 2146; https://doi.org/10.3390/ma11112146 - 31 Oct 2018

Cited by 14 | Viewed by 3039

Abstract

Investigation of the quaternary system, Ca–Eu–Cd–Sb, led to a discovery of the new solid solutions, Ca_1−xEu_xCd₂Sb₂, with the CaAl₂Si₂ structure type (x ≈ 0.3–0.9, hP5, P

\bar{3}

m [...] Read more.

Investigation of the quaternary system, Ca–Eu–Cd–Sb, led to a discovery of the new solid solutions, Ca_1−xEu_xCd₂Sb₂, with the CaAl₂Si₂ structure type (x ≈ 0.3–0.9, hP5, P

\bar{3}

m1, a = 4.6632(5)–4.6934(3) Å, c = 7.630(1)–7.7062(7) Å), Ca_2−xEu_xCdSb₂ with the Yb₂CdSb₂ type (x ≈ 0.6, oS20, Cmc2₁, a = 4.646(2) Å, b = 17.733(7) Å, c = 7.283(3) Å), and Eu_11−xCa_xCd₆Sb₁₂ with the Sr₁₁Cd₆Sb₁₂ type (x ≈ 1, mS58, C2/m, a = 32.407(4) Å, b = 4.7248(5) Å, c = 12.377(1) Å, β = 109.96(1)°). Systematic crystallographic studies of the Ca_1−xEu_xCd₂Sb₂ series indicated expansion of the unit cell upon an increase in the Eu content, in accordance with a larger ionic radius of Eu²⁺ vs. Ca²⁺. The Ca_2−xEu_xCdSb₂ composition with x ≈ 0.6 adopts the non-centrosymmetric space group, Cmc2₁, although the parent ternary phase, Ca₂CdSb₂, crystallizes in the centrosymmetric space group, Pnma. Two non-equivalent Ca sites in the layered crystal structure of Ca_2−xEu_xCdSb₂ get unevenly occupied by Eu, with a preference for the interlayer position, which offers a larger available volume. Similar size-driven preferred occupation is observed in the Eu_11−xCa_xCd₆Sb₁₂ solid solution with x ≈ 1. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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12 pages, 37384 KiB

Open AccessArticle

Structure and Chemical Bonding of the Li-Doped Polar Intermetallic RE₂In_1−xLi_xGe₂ (RE = La, Nd, Sm, Gd; x = 0.13, 0.28, 0.43, 0.53) System

by Junsu Lee, Jieun Jeon and Tae-Soo You

Materials 2018, 11(4), 495; https://doi.org/10.3390/ma11040495 - 26 Mar 2018

Cited by 3 | Viewed by 3203

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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Review

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22 pages, 6808 KiB

Open AccessFeature PaperReview

Zintl Phases as Reactive Precursors for Synthesis of Novel Silicon and Germanium-Based Materials

by Matt Beekman, Susan M. Kauzlarich, Luke Doherty and George S. Nolas

Materials 2019, 12(7), 1139; https://doi.org/10.3390/ma12071139 - 08 Apr 2019

Cited by 38 | Viewed by 6100

Abstract

Recent experimental and theoretical work has demonstrated significant potential to tune the properties of silicon and germanium by adjusting the mesostructure, nanostructure, and/or crystalline structure of these group 14 elements. Despite the promise to achieve enhanced functionality with these already technologically important elements, [...] Read more.

Recent experimental and theoretical work has demonstrated significant potential to tune the properties of silicon and germanium by adjusting the mesostructure, nanostructure, and/or crystalline structure of these group 14 elements. Despite the promise to achieve enhanced functionality with these already technologically important elements, a significant challenge lies in the identification of effective synthetic approaches that can access metastable silicon and germanium-based extended solids with a particular crystal structure or specific nano/meso-structured features. In this context, the class of intermetallic compounds known as Zintl phases has provided a platform for discovery of novel silicon and germanium-based materials. This review highlights some of the ways in which silicon and germanium-based Zintl phases have been utilized as precursors in innovative approaches to synthesize new crystalline modifications, nanoparticles, nanosheets, and mesostructured and nanoporous extended solids with properties that can be very different from the ground states of the elements. Full article

(This article belongs to the Special Issue Advances in Zintl Phases)

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