Structural diversity of the Zintl pnictides with rare-earth metals

Baranets, Sviatoslav; Ovchinnikov, Alexander; Bobev, Svilen

doi:10.1016/bs.hpcre.2021.07.001

Cited by 18 publications

(24 citation statements)

References 528 publications

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“…One family of compounds that were originally discovered by exploratory materials synthesis in metal fluxes are the AE 2 TPn 2 ( AE = Ca, Sr., Ba, Eu, Yb; T = Cd, Zn; Pn = P, As, Sb) Zintl phases. They are often dubbed as “2–1–2” and have been extensively studied over the last 10–15 years. − Their crystal structures feature different structural modifications in both hexagonal and orthorhombic symmetries, with the latter being generally related to the “9–4–9” phases. , A more detailed description of the compositional and structural diversities between the “2–1–2” phases has been reported elsewhere. , The inherent structural complexities in the various adopted crystal structures are known to drive their intrinsic low thermal conductivity, which is advantageous for thermoelectric materials studies and development.…”

Section: Introductionmentioning

confidence: 99%

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca₂CdSb₂ with a Non-centrosymmetric Monoclinic Structure

2022

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The Zintl phase Ca2CdSb2 was found to be dimorphic. Besides the orthorhombic Ca2CdSb2 (-o), here we report on the synthesis, the structural characterization, and the thermoelectric transport properties of its monoclinic form, Ca2CdSb2 (-m), and its Lu-doped variant Ca2–x Lu x CdSb2 (x ≈ 0.02). The monoclinic structure exhibits complex structural characteristics and constitutes a new structure type with the non-centrosymmetric space group Cm (Z = 30). The electrical resistivity ρ(T) measured on single crystals of both phases portrays a transition from a semiconductor to a degenerate p-type semiconductor upon doping with Lu and with an attendant change in the Hall carrier concentration n H from 7.15 × 1018 to 2.30 × 1019 cm–3 at 300 K. The Seebeck coefficient S(T) of both phases are comparable and indicate a hole-dominated carrier transport mechanism with magnitudes of 133 and 116 μV/K at 600 K for Ca2CdSb2 (-m) and Ca2–x Lu x CdSb2, respectively. The convoluted atomic bonding with an attendant large unit cell volume of ∼4365 Å3 drives a putative low thermal conductivity in these materials resulting in a power factor PF of 1.63 μW/cm K2 and an estimated thermoelectric figure of merit zT of ∼0.5 for Ca2–x Lu x CdSb2 at 600 K. Differential scanning calorimetry results reveal the stability of these phases up to about 960 K, making them candidates for moderate temperature thermoelectric materials.

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Section: Introductionmentioning

confidence: 99%

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca₂CdSb₂ with a Non-centrosymmetric Monoclinic Structure

2022

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“…Over the past decade, there has been a considerable research effort into synthesizing and characterizing Zintl compounds within the M –Zn– Pn (M = Ca, Sr, Ba, Eu, and Yb; Pn = P, As, Sb, and Bi) ternary phase spaces. The results of these inquires have been documented in many papers on the realization of both of unusual properties − and structures. − Under this broad umbrella of compounds that have been explored, perhaps the most substantial effort has been dedicated to researching “1–2–2” phasesone of the most abundant groups of ternary Zintl compounds. Compounds with general formulas MX 2 Pn 2 are known to form in a variety of structure types, encompassing a large range of elemental compositions (X = metal in a divalent state).…”

Section: Introductionmentioning

confidence: 99%

Two Polymorphs of BaZn₂P₂: Crystal Structures, Phase Transition, and Transport Properties

et al. 2021

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The novel α-BaZn2P2 structural polymorph has been synthesized and structurally characterized for the first time. Its structure, elucidated from single crystal X-ray diffraction, indicates that the compound crystallizes in the orthorhombic α-BaCu2S2 structure type, with unit cell parameters a = 9.7567(14) Å, b = 4.1266(6) Å, and c = 10.6000(15) Å. With β-BaZn2P2 being previously identified as belonging to the ThCr2Si2 family and with the precedent of structural phase transitions between the α-BaCu2S2 type and the ThCr2Si2 type, the potential for the pattern to be extended to the two different structural forms of BaZn2P2 was explored. Thermal analysis suggests that a first-order phase transition occurs at ∼1123 K, whereby the low-temperature orthorhombic α-phase transforms to a high-temperature tetragonal β-BaZn2P2, the structure of which was also studied and confirmed by single-crystal X-ray diffraction. Preliminary transport properties and band structure calculations indicate that α-BaZn2P2 is a p-type, narrow-gap semiconductor with a direct bandgap of 0.5 eV, which is an order of magnitude lower than the calculated indirect bandgap for the β-BaZn2P2 phase. The Seebeck coefficient, S(T), for the material increases steadily from the room temperature value of 119 μV/K to 184 μV/K at 600 K. The electrical resistivity (ρ) of α-BaZn2P2 is relatively high, on the order of 40 mΩ·cm, and the ρ(T) dependence shows gradual decrease upon heating. Such behavior is comparable to those of the typical semimetals or degenerate semiconductors.

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“…In the quest to identify new TE materials, the Zintl phases have drawn a lot of patronage over the years. − Notable among the Zintl phases with excellent TE properties are Yb 14 MnSb 11 , Ca 9 Zn 4+ x Sb 9 , and YbCd 2– x Zn x Sb 2 with zT > 1. This class of materials provides a rich platform for discovering new candidate materials that may be amenable for optimizing zT over a wide temperature range.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Transport Properties of the Family of Zintl Phases Ca₃RESb₃ (RE = La–Nd, Sm, Gd–Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance

2021

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Zintl phases with complex crystal structures have been studied as promising candidate materials for thermoelectric (TE) applications. Here, we report the syntheses of the family of rare-earth metal Zintl phases with the general formula Ca 4−x RE x Sb 3 (x ≈ 1; RE = La−Nd, Sm, Gd−Tm, Lu). The structural elucidation is based on refinements of single-crystal X-ray diffraction data for 12 unique chemical compositions. The cubic structure is confirmed as belonging to the anti-Th 3 P 4 structure type (space group I4̅ 3d, no. 220, Z = 4), where the Ca and RE atoms share the same atomic site with ca. 75 and 25% occupancies, respectively. Such crystallographic disordering of divalent Ca and trivalent RE atoms in the structure provides a pathway to intricate bonding. The latter, together with the presence of heavy elements such as Sb and the lanthanides, are expected to enhance the scattering probability of phonons, thereby leading to low thermal conductivity κ comparable to that of the ordered RE 4 Sb 3 . The drive of the hypothetical parent compound Ca 4 Sb 3 to be stabilized by alloying with rare-earth metals can be understood following the Zintl−Klemm concept, as the resultant formula may be rationalized as (Ca 2+ ) 3 RE 3+ (Sb 3− ) 3 , indicating the realization of closed-shell electronic configurations for all elements. This notion is confirmed by electronic structure calculations, which reveal narrow bandgaps E g = 0.77 and 0.53 eV for Ca 3 LaSb 3 and Ca 3 LuSb 3 , respectively. In addition, the incorporation of RE atoms into the structure drives the phase into a state of a degenerate semiconductor with dominant hole charge carriers.

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Structural diversity of the Zintl pnictides with rare-earth metals

Cited by 18 publications

References 528 publications

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca₂CdSb₂ with a Non-centrosymmetric Monoclinic Structure

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca₂CdSb₂ with a Non-centrosymmetric Monoclinic Structure

Two Polymorphs of BaZn₂P₂: Crystal Structures, Phase Transition, and Transport Properties

Synthesis and Transport Properties of the Family of Zintl Phases Ca₃RESb₃ (RE = La–Nd, Sm, Gd–Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance

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Structural diversity of the Zintl pnictides with rare-earth metals

Cited by 18 publications

References 528 publications

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca2CdSb2 with a Non-centrosymmetric Monoclinic Structure

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca2CdSb2 with a Non-centrosymmetric Monoclinic Structure

Two Polymorphs of BaZn2P2: Crystal Structures, Phase Transition, and Transport Properties

Synthesis and Transport Properties of the Family of Zintl Phases Ca3RESb3 (RE = La–Nd, Sm, Gd–Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance

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Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca₂CdSb₂ with a Non-centrosymmetric Monoclinic Structure

Structural Complexity and Tuned Thermoelectric Properties of a Polymorph of the Zintl Phase Ca₂CdSb₂ with a Non-centrosymmetric Monoclinic Structure

Two Polymorphs of BaZn₂P₂: Crystal Structures, Phase Transition, and Transport Properties

Synthesis and Transport Properties of the Family of Zintl Phases Ca₃RESb₃ (RE = La–Nd, Sm, Gd–Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance