Cs₂M^IIM^IV₃Q₈ (Q = S, Se, Te): An Extensive Family of Layered Semiconductors with Diverse Band Gaps

Abstract

Flame-melting rapid-cooling reactions were used to synthesize a number of pure phases of the Cs2MIIMIV 3Q8 family (MII = Mg, Zn, Cd, Hg; MIV = Ge, Sn; Q = S, Se, Te) whereas the more toxic members were synthesized using a traditional tube furnace synthesis. All Cs2MIIMIV 3Q8 compounds presented here crystallize in the noncentrosymmetric space group P212121, except for Cs2ZnGe3S8, which crystallizes in the centrosymmetric space group P21/n. The structures contain chains of corner-sharing MIIQ4 and MIVQ4 tetrahedra linked by edge-sharing MIV 2Q6 dimers to give a two-dimensional structure. All phases are structurally similar to the AMIIIMIVQ4 (A = alkali metal, Tl; MIII = Al, Ga, In; MIV = Si, Ge, Sn; Q = S, Se) phases; however, the members of this family have completely ordered MII and MIV sites as opposed to the occupational disorder of MIII and MIV over all tetrahedral sites present in AMIIIMIVQ4. The structural trends of the Cs2MIIMIV 3Q8 family are discussed, along with a systematic study of their optical properties. Density functional theory (DFT) electronic structure calculations were performed using the projector augmented wave method to further investigate the trends in the band gaps of the Cs2MIIMIV 3Se8 (MII = Mg, Zn; MIV = Ge, Sn) compounds. The experimental diffuse reflectance UV–vis spectroscopy results show that the Mg compounds have smaller band gaps than those containing Zn for both the Ge and the Sn families whereas the DFT calculations show the opposite trend. Cs2HgSn3Se8 was studied as a representative example of this family using differential thermal analysis and melts congruently at 595 °C. Crystal growth of this compound using the Bridgman method resulted in a polycrystalline ingot from which plate crystals ∼2 mm × 3 mm could be cleaved. The band gap of the compounds varies from a narrow 1.07 eV for Cs2ZnGe3Te8 to a wide 3.3 eV for Cs2ZnGe3S8 and Cs2CdGe3S8 making this family a potentially useful source of materials for a variety of electronic applications. Cs2HgSn3Se8 crystals exhibit photoconductivity response where the photoexcited electron and hole show mobility-lifetime products on the order of 3.69 × 10–5 cm2/V and (μτ)h∥ = 7.78 × 10–5 cm2/V, respectively.

Non‐centrosymmetric Selenides AZn4In5Se12 (A=Rb, Cs): Synthesis, Characterization and Nonlinear Optical Properties

“…The linear equation can be written as E g =9.43–0.0041 V . A similar behavior was observed in the Cs 2 X II X IV 3 Q 8 family . Such an interesting relationship between E g and V could shed some light on the prediction or design of new MFIR NLO compounds with excellent performance.…”

K2ZnSn3Se8: A Non‐Centrosymmetric Zinc Selenidostannate(IV) Featuring Interesting Covalently Bonded [ZnSn3Se8]2− Layer and Exhibiting Intriguing Second Harmonic Generation Activity

“…However, the trivalent and tetravalent metal sites in the KMM′Q 4 family are totally disordered, while in K 2 ZnSn 3 Se 8 , the bivalent metal Zn and tetravalent metal Sn occupy completely different sites. Additionally, it is worth noting that although a series of compounds in the A 2 MM′ 3 Q 8 (A=alkali metal; M=Mg, Zn, Cd, Hg; M′=Ge, Sn; Q=S, Se, Te) family have been reported, K 2 ZnSn 3 Se 8 is the first member in this family that crystallizes in the monoclinic space group P 2 1 (other compounds are mainly crystallized in space groups of ( P , P 2 1 / n , P 2 1 2 1 2 1 , Pa ). Recently, Rafael Besse et al.…”

“…It consists of special [ZnSn 3 Se 8 ] 2À layers that are perpendicular to the b axis with large interlayer voids occupied by K + .T he basic buildingu nit of each layer is a[ Zn 2 Sn 6 Se 20 ]b lock composed of corner-sharing ZnSe 4 and SnSe 4 tetrahedra, and an edge-sharing Sn 2 Se 6 dimer.T hese units propagate themselves along the c axis to form one-dimensional linear chains,a nd then the chains are linked side-by-side to generate as ingle layer.S imilar linkage pattern has also been found in the KMM'Q 4 (M = Ga, In;M ' = Ge, Sn;Q = S, Se) family, [19][20][21] examples include KGaSnS 4 ,K InGeS 4 ,K GaGeS 4 and b-KInSnSe 4 .H owever,t he trivalent and tetravalent metal sites in the KMM'Q 4 family are totally disordered, while in K 2 ZnSn 3 Se 8 ,t he bivalent metal Zn and tetravalent metal Sn occupy completelyd ifferent sites. Additionally,i ti sw orth noting that although as eries of compounds in the A 2 MM' 3 Q 8 (A = alkali metal;M= Mg, Zn, Cd, Hg;M ' = Ge, Sn;Q= S, Se, Te )f amily have been reported, [22,23] K 2 ZnSn 3 Se 8 is the first member in this familythat crystallizes in the monoclinic space group P2 1 (other compounds are mainly crystallized in space groups of (P 1 , P2 1 /n, P2 1 2 1 2 1 , Pa 3 ). Recently,R afael Besse et al have presented as ystematic investigation on the role of alkali and chalcogen atoms on the stability of the A 2 MM' 3 Q 8 family compounds.…”

“…Selected bond lengths for K 2 ZnSn 3 Se 8 are tabulated in Ta ble S2.A ll Zn and Sn atoms are tetrahedral coordinated to four Se atoms with the Zn-Se and Sn-Sebond lengths ranging from 2.4526(5)t o2 .5215(5) and 2.4682(4) to 2.5838(4) , respectively,c onsistent with those in other previously reported MCs. For example, the Zn-Se distances are in the range of 2.4712(1)-2.5253(6) ,2 .4615(1)-2.5798( 8) and 2.4668(1)-2.4802(1) in Cs 2 Bi 2 ZnSe 5 , [27] Ba 2 ZnSe 3 [28] and Cs 2 ZnSn 3 Se 8 , [23] respectively.T he Sn-Se distances are falling in the range of 2.4660(2) to 2.5967(3) for Li 2 SnSe 3 , [29] 2.4575(2) to 2.5804(2) for Cs 2 CdSn 3 Se 8 , [23] and 2.4835(5) to 2.5794 (5) for Cu 2 SnSe 3 , [30] respectively.T he Kc ations have two kinds of coordination environments (see Figure S1): K1 atoms are surrounded by eight Se atoms to form ab icapped triangular prism, whereas K2, K3 and K4 are coordinated by seven Se atoms, forming amonocapped triangular prism.…”

K2Hg2Se3: Large-Scale Synthesis of a Photoconductor Material Prototype with a Columnar Polyanionic Substructure

“…18 From a physical point of view, the presence of very heavy element atoms causes unique material properties, especially regarding thermoelectric or optoelectronic applications in sensors, which can be further adjusted by according variation of the elements within a family of structurally related compounds. 19 For reducing thermal conductivities, the addition of salt-like characteristics is desirable, e.g., by specific design of chalcogenidometalates. 20 For this, we are currently extensively investigating the system K/Hg/Ch (Ch = S, Se 24,25 or 3D-{[Hg 6 Ch 7 ] 2− } (Ch = S, Se) 25−27 anionic substructures were reported as wide-band gap semiconductors and discussed for band gap engineering.…”