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of transition metal oxidation states and occupancies for La6(TM)xSi2S14 (TM = most transition metals). Monovalent metals (x = 2) occupy the trigonal faces of the octahedra (a); for x = 1–0.5, the metals occupy the centers of the octahedra (b). For metals in red, we were unable to grow single crystals, therefore the oxidation state is attributed according to EDS data. For Ag literature data was used.⁵⁰ For metals with (*) bulk phase/single crystal growth failed for La–TM–Si–S composition, but there is indication of formation of the target quaternary phase with either other rare-earth metals or other tetrels. (**) For Re quaternary phase formation failed for all attempts with Si, Ge and Sn
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An innovative method of synthesis is reported for the large and diverse (RE)6(TM) x (Tt)2S14 (RE = rare-earth, TM = transition metals, Tt = Si, Ge, and Sn) family of compounds (∼1000 members, ∼325 contain Si), crystallizing in the noncentrosymmetric, chiral, and polar P63 space group. Traditional synthesis of such phases involves the annealing of e...
Citations
... We have recently shown the power of the mixing of refractory materials method when two refractory components are mixed by forming a binary compound via arc melting. The resulting compound is introduced into a reaction with more active components simultaneously and in close spatial proximity [52][53][54][55] . This method cannot be applied to Fe-B mixing due to the absence of boron-rich Fe borides. ...
A computational search for stable structures among both α and β phases of ternary ATB 4 borides ( A = Mg, Ca, Sr, Ba, Al, Ga, and Zn, T is 3d or 4d transition elements) has been performed. We found that α-ATB 4 compounds with A = Mg, Ca, Al, and T = V, Cr, Mn, Fe, Ni, and Co form a family of structurally stable or almost stable materials. These systems are metallic in non-magnetic states and characterized by the formation of the localized molecular-like state of 3d transition metal atom dimers, which leads to the appearance of numerous Van Hove singularities in the electronic spectrum. The closeness of such singularities to the Fermi level can be easily tuned by electron doping. For the atoms in the middle of the 3d row (Cr, Mn, and Fe), these singularities led to magnetic instabilities and magnetic ground states with a weakly metallic or semiconducting nature. Such states appear as non-trivial coexistence of the different spin ladders formed by magnetic dimers of 3d elements. These magnetic states can be characterized as an analog of the spin glass state. Experimental attempts to produce MgFeB 4 and associated challenges are discussed, and promising directions for further synthetic studies are formulated.
... Synthetic methodology which we developed for phosphides, includes reaction of phosphorus with atomically mixed refractory precursor, premelted M+Si, allowed the discovery of several previously inaccessible compounds. 2,18,19 In this work we extended this methodology to arsenides. Based on the ease of synthesis and discovery of the title compound, IrSi 3 As 3 , it is expected that many other metal tetrel arsenides exist with likewise exciting properties. ...
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....
... Nevertheless, the series of phase transformations can still be determined with high reliability which further aids synthesis efforts and our knowledge of solid state reaction mechanisms. [25][26][27][28] In situ XRD studies were previously shown to be useful for synthesis of novel boron-containing compounds. 29 In the studied synthesis of nickel boride, BI 3 amorphized or went into the gaseous phase at 359 K, leaving only Ni to be detected by powder XRD. ...
A facile and universal route for synthesizing transition metal borides has been developed by a reaction of boron triiodide (BI3) with elemental transition metals. This method employs relatively low synthesis...
... Quaternary sulfides of the type (RE) 6 (TM) x (T) 2 Q 14 (RE = rareearth; TM = transition metals; T=Si, Ge, Sn, Be, Fe, Zn, Sm, Yb, B, Al, Ga, and In; Q=S and Se) are a large class of compounds which adopt the non-centrosymmetric, polar, and chiral P6 3 space group. [11][12][13] For coinage metals (group 11) with + 1 oxidation state, x = 2 and the aforementioned formula (6-2-2-14) can be reduced to the (RE) 3 (TM)TQ 7 notation (3-1-1-7), which will be used below. La 3 CuGeS 7 was previously identified as a promising NLO material with good SHG and LDT properties compared to its analogues with T=Si or Sn and other transition metals. ...
... La 3 CuGeS 7 was previously identified as a promising NLO material with good SHG and LDT properties compared to its analogues with T=Si or Sn and other transition metals. [12] Using a principle of composition optimization in this prototype structure, it is possible to synthesize phases with better NLO properties. [14] By substituting La for rare-earth metals with smaller ionic radii (Y, Ce, Sm, and Gd), a change in the bond length and angles of the underlying polyhedral structure was observed, resulting in Gd 3 CuGeS 7 having the best combination of SHG (1.6 × AgGaS 2 at 88-105 μm particle size) and LDT (3 × AgGaS 2 ) and being phase matchable. ...
... To explore composition optimization, La 3 CuGeS 7 was chosen as a prototype structure for studying NLO properties (SHG and LDT) in the (RE) 6 (TM) x (T) 2 Q 14 family of chiral and polar quaternary sulfides. La 3 CuGeS 7 showed promising NLO properties as compared to analogous phases with Si or Sn in place of Ge and a variety of transition metals instead of Cu. [12] By substituting La for rare-earth metals with smaller ionic radii, a change in the bond length and angles of the underlying polyhedral structure was observed, with Gd 3 CuGeS 7 having the best combination of SHG (1.6 × AgGaS 2 at 88-105 μm particle size) and LDT (3 × AgGaS 2 ) and being phase matchable. Based on analysis of the crystal structures, it is proposed that the degree of distortion of GeS 4 tetrahedra (C 3v type elongation of one GeÀ S bond) as well as the coplanarity and flatness of [CuS 3 ] units are important factors for achieving high NLO characteristics in this family of materials. ...
Non‐linear optical materials must possess a balanced combination of laser‐induced damage threshold (LDT) and second‐harmonic generation (SHG) and be phase matchable. In our previous work, chiral and polar La3CuGeS7 was identified as promising non‐linear optical material. Herein, we report the optimization of non‐linear optical properties through replacement of La with smaller lanthanides. It is determined that Gd3CuGeS7 exhibits the best combination of SHG (1.6´ AgGaS2 at 88‐105 µm particle size) and LDT (3´ AgGaS2, 89 MW/cm2) and is phase matchable. Based on changes in transition metal‐sulfur bond lengths and angles, we further propose structural optimization through solid‐solution formation and doping.
... While all compounds with the La 3 CuSiS 7 structure have the possibility of demonstrating SHG due to their NCS structures, NLO studies were performed for only a few members of the family [35][36][37][42][43][44]. Sm 3 LiSiS 7 , isotypic to the compounds presented here, displays a strong, non-phase-matching (NPM) SHG response of 1.5 × AGS at 2.09 µm and a high LIDT of ~3.7 × AGS at 1.064 µm [35]. ...
... They suggested that the Ln coordination can be described as 7 + 1, where the CN can reach 8 depending on the ratio of c/a [55]. In the compounds with lower CNs, the eighth lanthanidechalcogen interaction lies outside the range of a reasonable bonding The average Si-S bond distance was found to be 2.123(5) Å, which agrees well with the average Si-S bond distances of 2.124(4) and 2.131(4) Å for the isostructural Sm 3 Al 0.33 SiS 7 [43] and La 3 Au 0.96 SiS 7 [44], respectively. ...
Eighteen isotypic, lithium-containing rare-earth sulfides, crystallizing in the chiral, polar, and noncentrosymmetric space group P63 with the La3CuSiS7-structure type have been prepared via direct-combination of the elements or binary sulfides; nine of these compounds are reported for the first time. The structures of these compounds, with the formulae Ln3LiTS7 (Ln=La, Ce, Pr, Nd, Sm, Gd, and Dy for T= Si or Ge; Ln = La, Ce, Pr, and Nd for T=Sn), were determined by single crystal X-ray diffraction. According to X-ray powder diffraction data, the Ln3LiTS7 compounds are the major phase of the reaction products. All of the compounds are semiconductors with optical bandgaps spanning nearly the entire visible region. The Si- and Ge-containing analogs show high thermal stability, >1000 °C, while the Sn-containing compounds melt in the vicinity of ~740 °C. The compounds show potentially broad regions of optical transparency in the infrared regime. Calculated bond valence sums (BVSs) and global instability index (G) values confirm the Ln³⁺ oxidation state and stable crystal structures with reasonable strain, respectively. Ce3LiGeS7 and Ce3LiSnS7 display non-phase-matching but significant second-harmonic generation responses with χ2 values of 21±1 and 28±1 pm/V, respectively at λ=1.8 μm. The laser-induced damage threshold values for Ce3LiGeS7 and Ce3LiSnS7 are >3 × commercial AgGaSe2, for picosecond pluses at λ=1.064 μm. These two compounds also exhibit moderate third-harmonic generation responses. Additionally, crystal-chemical correlations are discussed.
... (RE) 6 (TM) x Z 2 Q 14 (RE = rare-earth; TM = transition metals; Z = tetrels (Si, Ge, and Sn), triels (B, Al, Ga, and In) as well as some group II (Be), transition metals (Fe, Zn), and lanthanides (Sm and Yb); Q = S and Se) is a large class of compounds which crystallizes in the chiral, polar, and non-centrosymmetric P6 3 space group [11,12]. For simplicity, we will use Tt notation to describe compositions with Si and Ge. ...
... For simplicity, we will use Tt notation to describe compositions with Si and Ge. For (RE) 6 (TM) x (Tt) 2 Q 14 x = 2/n, where n is the oxidation state of the metal (TM n+ = Cu + , Li + , Mn 2+ , Rh 3+ , Hf 4+ , etc.) [12]. While these phases possess non-linear optical properties due to the noncentrosymmetric space group, the reason for the different values of SHG and LDT values of its members is not entirely understood. ...
... While these phases possess non-linear optical properties due to the noncentrosymmetric space group, the reason for the different values of SHG and LDT values of its members is not entirely understood. Among phases with trigonal planar TM-S geometry ([TM)S 3 ]), La 6 Cu 2 Ge 2 S 14 showed a good balance of SHG and LDT and phase matchability, while La 6 Cu 2 Si 2 S 14 showed poor SHG response [12]. For structures with octahedral [TM)S 6 ] units, SHG activity depends on the concentration, oxidation state, and spin state of the transition metal; for example, structures with low spin d 6 Rh 3+ (1/3 octahedra occupied) show better activity than those with Co 2+ located in ½ of all octahedra [12]. ...
Non-linear optical (NLO) materials require a balance of high second-harmonic generation (SHG) signal and laser damage threshold (LDT), as well as phase matchable behavior. Herein, we report a new member of the (RE)6(TM)x(Tt)2Q14 family of compounds, La6PdSi2S14, which, unlike all other reported TM analogues crystallizing in hexagonal P63 space group, crystallizes in the non-centrosymmetric monoclinic P21 space group. The crystal structure contains chains of edge-sharing distorted square planar [PdS4] units. The square-planar coordination of Pd in La6PdSi2S14 exhibits remarkable NLO properties with high SHG (3.7 × AgGaS2) and LDT (3 × AgGaS2) values as well as phase matchability. This shows the promise of novel materials with distorted structural motifs for enhanced NLO properties. Upon formation of bimetallic chiral sulfides containing both Cu and Pd, Cu occupies the opposite faces of the octahedra forming [CuS3] units while Pd can be stabilized in the center of PdS6 octahedra in the hexagonal P63 crystal structure of La6Pd0.5CuSi2S14. This suggests that it is possible to form mixed metal systems which could further enhance NLO properties by incorporation of additional structural distortions.
With the continuous development of laser technology and the increasing demand for lasers of different frequencies in the infrared (IR) spectrum, research on infrared nonlinear optical (NLO) crystals has garnered growing attention. Currently, the three main commercially available types of borate materials each have their drawbacks, which limit their applications in various areas. Rare-earth (RE)-based chalcogenide compounds, characterized by the unique f-electron configuration, strong positive charges, and high coordination numbers of RE cations, often exhibit distinctive optical responses. In the field of IR-NLO crystals, they have a research history spanning several decades, with increasing interest. However, there is currently no comprehensive review summarizing and analyzing these promising compounds. In this review, we categorize 85 representative examples out of more than 400 non-centrosymmetric (NCS) compounds into four classes based on the connection of different asymmetric building motifs: (1) RE-based chalcogenides containing tetrahedral motifs; (2) RE-based chalcogenides containing lone-pair-electron motifs; (3) RE-based chalcogenides containing [BS3] and [P2Q6] motifs; and (4) RE-based chalcohalides and oxychalcogenides. We provide detailed discussions on their synthesis methods, structures, optical properties, and structure–performance relationships. Finally, we present several favorable suggestions to further explore RE-based chalcogenide compounds. These suggestions aim to approach these compounds from a new perspective in the field of structural chemistry and potentially uncover hidden treasures within the extensive accumulation of previous research.
Nonlinear optical (NLO) materials are an interesting class of compounds that have found application in many aspects of our ordinary lives. Solid-state NLO materials can be classified into organic, inorganic, and hybrid. This brief review article has the aim of introducing the readers to the fundamental principles of nonlinear optics while focusing on the inorganic solid-state NLO materials with an emphasis on their structural peculiarities, synthetic methods, and applications. The materials will be grouped by their intended spectral application: mid- and far-IR (chalcogenides, halides, and pnictides), near-IR and visible ranges (KDP, KTP and iodates), and UV and deep-UV (borates, carbonates, nitrates, and phosphates). Among the compounds that are discussed, several classes are highlighted: promising IR compounds with wide band gaps (Eg > 3.5 eV) with second harmonic generation (SHG) coefficients comparable to industry standard AgGaS2 (dij ≥ 1 × AGS) suitable for mid-IR NLO applications, NLO compounds that can meet commercial requirements in the vis-NIR and UV regions, and deep-UV materials with even wider band gaps (Eg > 6.2 eV) and SHG coefficients surpassing those of traditional KH2PO4 crystals (dij ≥ 1 × KDP). Several prevailing synthetic methods (solid-state, flux, and hydrothermal) are discussed, and different types of characterization techniques are presented. Finally, applications, ranging from lasers and quantum and neuromorphic computing to “uses beyond optics” in battery electrodes and ionic conductors are discussed. Although brief, we hope this review will provide valuable insights into the fast-expanding field of solid-state NLO materials.
Structural dissymmetry and strong second‐harmonic generation (SHG) responses are key conditions for nonlinear optical (NLO) crystals, and targeted combinatorial screening of suitable anionic groups has become extremely effective. Herein, optimal combination of flexible SnSn (n = 5, 6) groups and highly electropositive cations (lanthanides (Ln³⁺) and alkaline earth (Ae²⁺: Sr, Ca) metals) affords the successful synthesis of 12 NLO thiostannates including Ln2Sr3Sn3S12 (Pmc21) and Ln2Ca3Sn3S12 (P‐62m); whereas 17 rigid GeS4 or SiS4 tetrahedra‐constructed Ln2Ae3Ge3S12 and Ln2Ae3Si3S12 crystallize in the centrosymmetric (CS) Pnma. This unprecedented CS to noncentrosymmetric (NCS) structural transformation (Pnma to P‐62m to Pmc21) in the Ln2Ae3MIV3S12 family indicates that chemical substitution of the tetrahedral GeS4/SiS4 units with SnSn breaks the original symmetry to form the requisite NCS structures. Remarkably, strong polarization anisotropy and hyperpolarizability of the Sn⁽⁴⁺⁾S5 unit afford huge performance improvement from the nonphase‐matching (NPM) SHG response (1.4 × AgGaS2 and Δn = 0.008) of La2Ca3Sn3S12 to the strong phase‐matching (PM) SHG effect (3.0 × AgGaS2 and Δn = 0.086) of La2Sr3Sn3S12. Therefore, Sn⁽⁴⁺⁾S5 is proven to be a promising “NLO‐active unit.” This study verifies that the coupling of flexible SnSn building blocks into structures opens a feasible path for designing targeted NCS crystals with strong nonlinearity and optical anisotropy.
