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  1. Noncentrosymmetric (NCS) silicon phosphides have recently shown promise as nonlinear optical materials due to the balance of strong second harmonic generation (SHG) activity and large laser damage threshold (LDT) values. While arsenides of electropositive metals, such as Ba, Mg, Zn, and Cd were explored, no NLO properties for transition metal tetrel arsenides have yet been reported. IrSi 3 As 3 is a novel compound, isostructural to IrSi 3 P 3 , which allows a direct investigation on the impact of the heavier pnictogen on structural and optical properties. The direct bandgap is reduced from 1.8 eV for IrSi 3 P 3 to 1.55 eV for IrSi 3 As 3 . Unlike many NLO chalcogenides, IrSi 3 As 3 has a small bandgap without compromising the balance between SHG signal and high LDT values. IrSi 3 As 3 was found to outperform both its phosphide analogue IrSi 3 P 3 , as well as the state-of-the-art infrared SHG standard AgGaS 2 (AGS) in SHG activity and the LDT. 
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    Free, publicly-accessible full text available June 6, 2024
  2. Free, publicly-accessible full text available July 25, 2024
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    The unconventional clathrates, Cs 8 Zn 18 Sb 28 and Cs 8 Cd 18 Sb 28 , were synthesized and reinvestigated. These clathrates exhibit unique and extensive superstructural ordering of the clathrate-I structure that was not initially reported. Cs 8 Cd 18 Sb 28 orders in the Ia 3̄ d space group (no. 230) with 8 times larger volume of the unit cell in which most framework atoms segregate into distinct Cd and Sb sites. The structure of Cs 8 Zn 18 Sb 28 is much more complicated, with an 18-fold increase of unit cell volume accompanied by significant reduction of symmetry down to P 2 (no. 3) monoclinic space group. This structure was revealed by a combination of synchrotron X-ray diffraction and electron microscopy techniques. A full solid solution, Cs 8 Zn 18−x Cd x Sb 28 , was also synthesized and characterized. These compounds follow Vegard's law in regard to their primitive unit cell sizes and melting points. Variable temperature in situ synchrotron powder X-ray diffraction was used to study the formation and melting of Cs 8 Zn 18 Sb 28 . Due to the heavy elements comprising clathrate framework and the complex structural ordering, the synthesized clathrates exhibit ultralow thermal conductivities, all under 0.8 W m −1 K −1 at room temperature. Cs 8 Zn 9 Cd 9 Sb 28 and Cs 8 Zn 4.5 Cd 13.5 Sb 28 both have total thermal conductivities of 0.49 W m −1 K −1 at room temperature, among the lowest reported for any clathrate. Cs 8 Zn 18 Sb 28 has typical p-type semiconducting charge transport properties, while the remaining clathrates show unusual n–p transitions or sharp increases of thermopower at low temperatures. Estimations of the bandgaps as activation energy for resistivity dependences show an anomalous widening and then shrinking of the bandgap with increasing Cd-content. 
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  4. Abstract

    A new compound NaCd4Sb3(Rm,a=4.7013(1) Å,c=35.325(1), Å, Z=3,T=100 K) featuring the RbCd4As3structure type has been discovered in the Na−Cd−Sb system, in addition to the previously reported NaCdSb phase. NaCd4Sb3and NaCdSb were herein synthesized using sodium hydride as the source of sodium. The hydride method allows for targeted sample composition, improved precursor mixing, and an overall quicker synthesis time when compared to traditional methods using Na metal as a precursor. The NaCd4Sb3structure was determined from single‐crystal X‐ray diffraction and contained the splitting of a Cd site not seen in previous isostructural phases. NaCd4Sb3decomposes into NaCdSb plus melt at 766 K, as determined viain‐situhigh‐temperature PXRD. The electronic structure calculations predict the NaCd4Sb3phase to be semi‐metallic, which compliments the measured thermoelectric property data, indicative of ap‐type semi‐metallic material. The crystal structure, elemental analysis, thermal properties, and electronic structure are herein discussed in further detail.

     
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  5. Abstract

    The compositional screening of K‐Zn‐Sb ternary system aided by machine learning, rapid exploratory synthesis using KH salt‐like precursor and in situ powder X‐ray diffraction yielded a novel clathrate type XI K58Zn122Sb207. This clathrate consists of a 3D Zn‐Sb framework hosting K+ions inside polyhedral cages, some of which are reminiscent of known clathrate types while others are unique to this structure type. The complex non‐centrosymmetric structure in the tetragonal space groupwas solved by means of single crystal X‐ray diffraction as a 6‐component twin due to pseudocubic symmetry and further confirmed by high‐resolution synchrotron powder X‐ray diffraction and state‐of‐the‐art scanning transmission electron microscopy. The electron‐precise composition of this clathrate yields narrow‐gapp‐type semiconductor with extraordinarily low thermal conductivity due to displacement or “rattling” of K cations inside oversized cages and as well as to twinning, stacking faults and antiphase boundary defects.

     
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  6. Abstract

    The compositional screening of K‐Zn‐Sb ternary system aided by machine learning, rapid exploratory synthesis using KH salt‐like precursor and in situ powder X‐ray diffraction yielded a novel clathrate type XI K58Zn122Sb207. This clathrate consists of a 3D Zn‐Sb framework hosting K+ions inside polyhedral cages, some of which are reminiscent of known clathrate types while others are unique to this structure type. The complex non‐centrosymmetric structure in the tetragonal space groupwas solved by means of single crystal X‐ray diffraction as a 6‐component twin due to pseudocubic symmetry and further confirmed by high‐resolution synchrotron powder X‐ray diffraction and state‐of‐the‐art scanning transmission electron microscopy. The electron‐precise composition of this clathrate yields narrow‐gapp‐type semiconductor with extraordinarily low thermal conductivity due to displacement or “rattling” of K cations inside oversized cages and as well as to twinning, stacking faults and antiphase boundary defects.

     
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