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Article

Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7

by
Craig Cropek
1,
Vivian Nguyen
1,
Santosh Karki Chhetri
2,
Jin Hu
2,3,
Shengping Guo
4 and
Jian Wang
1,*
1
Department of Chemistry and Biochemistry, Wichita State University, Wichita, KS 67260, USA
2
Department of Physics, University of Arkansas, Fayetteville, AR 72701, USA
3
Materials Science and Engineering Program, Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, AR 72701, USA
4
School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China
*
Author to whom correspondence should be addressed.
Crystals 2022, 12(11), 1505; https://doi.org/10.3390/cryst12111505
Submission received: 22 September 2022 / Revised: 14 October 2022 / Accepted: 19 October 2022 / Published: 22 October 2022
(This article belongs to the Special Issue Recent Advances in Nonlinear Optical Crystals)
Browse Figures
Versions Notes

Abstract

:
Two thiophosphates, KInP2S7 and KCrP2S7, were structurally characterized without investigating any optical properties. Herein in this work, KInP2S7 and KCrP2S7 were revisited to investigate their optical and magnetic properties, respectively. Pure polycrystalline samples and crystals of KInP2S7 and KCrP2S7 were grown by high temperature solid state reactions, where mm-sized crystals of KCrP2S7 were collected. KCrP2S7 is isostructural to KInP2S7, which features a layered structure. KInP2S7 and KCrP2S7 possess close relationship to the layered thiophosphate M2P2S6 (M = Fe, Co, Zn, etc.). The bonding pictures of KInP2S7 were studied using the electron localization function (ELF) coupled with crystal orbital Hamilton population (COHP) calculations. The intrinsically distorted [PS4] tetrahedra and [InS6] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. Electronic structure analysis confirmed that the optical properties of KInP2S7 are mainly contributed to by [PS4] tetrahedra together with small amounts of the contributions coming from [InS6] octahedra. Magnetic measurement on mm-sized crystals of KCrP2S7 verified that there is an antiferromagnetic transition around 21 K, and the Cr atoms are trivalent. KInP2S7 is predicated to be an indirect bandgap semiconductor of 2.38 eV, which is confirmed by the UV-Vis measurement of 2.4(1) eV. KInP2S7 is not a type-I phase-matching material and exhibits moderate second harmonic generation (SHG) response (0.51 × AgGaS2, sample of particle size of 100 µm). The laser damage threshold (LDT) of KInP2S7 is very high of 5.2 × AgGaS2. Bandgap engineering were undergone to enhance the SHG response of KInP2S7.

1. Introduction

Thiophosphates, which are constructed by phosphorus and sulfur atoms, have attracted growing interests due to important applications such as nonlinear optical applications [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16], ion conductors [17,18,19,20,21,22,23,24,25,26], hydrogen evolution [27,28], and photocurrent response [29]. The chemical flexibility of thiophosphates accounts for their fruitful applications. The chemical flexibility originates from flexible crystal structures spanning from three dimensional (3D) frameworks [25,30], two-dimensional layered structures [31], and one-dimensional chain structures [32]. Phosphorus and sulfur elements share many similar properties such as low melting points, high volatile nature and easily form homoatomic bonds, etc. There exist significant different properties between phosphorus and sulfur, for example, electron configuration and electronegativity. The phosphorus atoms are surrounded by four sulfur atoms forming a tetrahedron, which are interconnected via the sharing of apex sulfur atoms, homoatomic P-P bonds, or homoatomic S-S bonds to form various [PxSy] motifs [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. The flexible [PxSy] motifs, interacting with metals, generate the flexible structures of thiophosphates [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16].
An acentric thiophosphate group, AIIIP2S7 (A = K, Rb, Cs; III = V, Cr, In) [33,34,35,36,37] has attracted our attention due to their interesting structures and the presence of both transition metals and main group elements within one system. The trivalent transition metals V3+ and Cr3+ possess unpaired d-electrons, which introduces magnetic properties into the AIIIP2S7 family. The crystal structures of AIIIP2S7 were studied by few groups. To the best of our knowledge, there were no systemic study of synthesis, electronic structure, bonding pictures, and nonlinear optical properties of the AIIIP2S7 family, reported. A previous study found interesting magnetic properties of KV1−xCrxP2S7 (X = 0, 0.75, 1), where KBr was utilized as a transport agent and a source of K [37]. In this work, we selected KInP2S7 and KCrP2S7 from the AIIIP2S7 family as our study objectives. A systematic study of synthesis, electronic structure, bonding pictures, and nonlinear optical properties of KInP2S7 are presented in this work. A detailed magnetic study of KCrP2S7, based on crystals grown from solid state reactions, were carried out, which resulted in the findings of the presence of an antiferromagnetic transition around 21 K. KInP2S7 was found as an indirect semiconductor of a bandgap of 2.38 eV and 2.4(1) eV, supported by tight-binding calculations and UV-Vis measurements, respectively. The Nonlinear optical properties of KInP2S7 were also measured in this work. The electronic structure and bonding picture studies of KInP2S7 were also studied in this work.

2. Materials and Methods

2.1. Synthesis

All starting materials were used as received without further processing, except for the cutting of solid metals: Potassium metal (Thermo Fisher Scientific, Waltham, MA, USA, 99.5%, indium shot metal basis (Thermo Fisher Scientific, MA, USA, 99.9%), chromium powder (Sigma-Aldrich, St. Louis, MO, USA, 99.5%), phosphorus powder (Alfa Aesar, Ward Hill, MA, USA, 99.5%), sulfur powder (Thermo Fisher Scientific, MA, USA, 99.5%). These reactants were stored in an argon-filled glovebox. Moisture and oxygen levels are maintained below 0.5 ppm. All preparations were done in a glovebox and sealed under a vacuum. All quartz ampoules were sealed under 100 mTorr.

2.1.1. KCrP2S7 Single Crystal Growth

0.4000 g of reactants were loaded into a 9 mm inner-diameter carbonized silica ampoule at a stoichiometric ratio of K:Cr:P:S = 1:1:2:7. Potassium was rolled in pre-weighed chromium powder before adding to the ampoule. After sealing, these reactants were loaded into a programmable muffle furnace. The reactants were heated from room temperature to 125 °C in 10 h, dwelled for 10 h, heated up to 700 °C in 10 h, dwelled for 96 h, and then cooled to room temperature in 24 h. High quality large black needles were obtained. Formation of KCrP2S7 was verified using powder X-ray diffraction (vide infra).

2.1.2. KInP2S7

0.5000 g total of reactants were loaded into a 9 mm inner-diameter carbonized silica ampoule at a stoichiometric ratio of K:In:P2S5:S = 1.2:1:1:2, and in that order. P2S5 was grown as a single phase via heating stoichiometric ratio of P and S at 350 °C for 24 h. Ampoules were capped using parafilm and then pumped out of the glovebox for sealing. The ampules were sealed to an inner-ampoule length of about 8.3 cm. After sealing the ampoules, they were placed vertically in a programmable muffle furnace and separated, by about 2.5 cm, in individual ampoule holders held in a homemade quartz holder setup. The reactants were heated from room temperature to 125 °C in 10 h, dwelled for 10 h, heated up to 650 °C in 10 h, dwelled for 96 h, ramped down for 24 h to room temperature. A second annealing process was necessary to improve the phase purity. Amber single crystals and an amber colored mass was obtained. Formation of KInP2S7 was verified using powder X-ray diffraction (Figure S1). KInP2S7 and KCrP2S7 were stable in dry air for a few weeks. Within a high moisture environment, KInP2S7 and KCrP2S7 would slowly decompose into amorphous products.

2.2. Powder X-ray Diffraction

Powder X-ray diffraction data were collected at room temperature using a Rigaku Mini Flex VI diffractometer with Cu-Kα radiation (λ = 1.5406 Å) in the range 2θ = 10°–80°, at a scan step of 0.04° with ten seconds exposure time.

2.3. UV-Vis Measurements

Diffuse-reflectance spectra were recorded at room temperature by a PERSEE-T8DCS UV-Vis spectrophotometer equipped with an integration sphere in the wavelength range of 230−850 nm. The reflectance data, R were recorded and converted to the Kubelka-Munk function, f(R) = (1 − R)2(2R)−1. The Tauc plots, (KM × E)2 and (KM × E)1/2, were applied to estimate direct and indirect bandgaps, respectively.

2.4. Second Harmonic Measurements

Using the Kurtz and Perry method [38], powder SHG responses of KInP2S7 compound were investigated by a Q-switch laser (2.09 μm, 3 Hz, 50 ns) with various particle sizes, including 38.5–54, 54–88, 88–105, 105–150, and 150–200 μm. Homemade AgGaS2 was selected as the reference. The lab-synthesized AgGaS2 crystals were ground to the same size range as KInP2S7. The LDTs of the title compounds were evaluated on powder samples (150−200 μm) with a pulsed YAG laser (1.06 μm, 10 ns, 10 Hz). The judgment criterion is as follows: with increasing laser energy, the color change of the powder sample is constantly observed by an optical microscope to determine the damage threshold. To adjust different laser beams, an optical concave lens is added to the laser path. The damaged spot is measured by the scale of the optical microscope.

2.5. TB-LMTO-ASA Calculations

The density of states (DOS), partial density of states (PDOS), band structure, crystal orbital Hamilton population (COHP), and electron localization function (ELF) of KInP2S7 are calculated using the tight binding-linear muffin tin orbitals-atomic sphere approximation (TB-LMTO-ASA) program [39,40]. The Barth-Hedin exchange potential was employed for the LDA calculations [39]. The radial scalar-relativistic Dirac equation was solved to obtain the partial waves. The basis set used contained K (4s), In (5s, 5p, 5d) P (3s, 3p) and S (3s, 3p) orbitals, and was employed for a self-consistent calculation, with downfolded functions of K (4p, 3d), In (4f, 5d), P (3d) and S (3d). The density of states and band structures were calculated after converging the total energy on a dense k-mesh of KInP2S7 (16 × 16 × 16 points with 2064 irreducible k-points).

2.6. Magnetic Properties Measurements

Temperature dependence of magnetic susceptibility and isothermal magnetization measurements were performed by using the ACMSII option of a physical properties measurement system (PPMS).

3. Results and Discussion

3.1. Synthesis and Crystal Growth

To reduce the chance of incorporating foreign elements, a high temperature solid state synthetic method was preferred in this study. Due to the high reactive nature of potassium metals, the bottom of silica tubes was protected by amorphous carbon. Large mm-sized single crystals of KCrP2S7 were collected as shown in Figure 1 inset. The powder X-ray diffraction results confirmed the single-phase nature of KCrP2S7 as shown in Figure 1. The large KCrP2S7 crystals were manually selected and cleaved for magnetic measurements (vide infra). Pure samples of KInP2S7 were also collected after a high temperature solid state reaction (Figure S1). The crystals of KInP2S7 did not grow as large as the KCrP2S7. The final products of KInP2S7 are a mixture of KInP2S7 small crystals and polycrystalline powder chunks.

3.2. Crystal Structures

KCrP2S7 is isostructural to KInP2S7, which both crystallizes in the LiFeAs2O7 structure type and the acentric C2 (no.5) space group [35]. The acentric nature of KInP2S7 is confirmed by SHG measurements (vide infra). To simplify the discussion, KInP2S7 is selected to present the structural chemistry. The structure of KInP2S7 is summarized in Figure 2b,d. KInP2S7 possesses clear layered features, which is constructed by two-dimensional (2D) [InP2S7]−slabs sandwiched by K+ cations. The detailed view of 2D [InP2S7]− slab is shown in Figure 2d. The 2D [InP2S7]− slab is built by [InS6] octahedra and [P2S7] units. The [InS6] octahedra are interconnected to the [P2S7] units via sharing edges and vertices. The [P2S7] units are made by two [PS4] tetrahedra via sharing one apex sulfur atom. Each In atom is in the center of a distorted octahedron with the In-S distance falling into the range of 2.581–2.698 Å [35]. The P-S distances within [PS4] tetrahedra are 2.005–2.137 Å, which are comparable to many thiophosphates such as α-Ba2P2S6 (1.99(2)–2.04(2) Å) [15], β-Ba2P2S6(2.017(2)–2.028(2) Å) [15], Pb2P2S6(2.011(19)–2.040(18) Å) [15], K2BaP2S6 (1.958(17)–2.066(15) Å) [41], KSbP2S6 (1.962(1)–2.077(1) Å) [42], KBiP2S6 (1.961(3)–2.059(3) Å) [43], Pb3P2S8 (2.031–2.065 Å) [44], etc.
One interesting point here would be the structure relationship between KInP2S7 and M2P2S6 (M = Mg, Mn, Fe, Co, Ni, Zn, Cd, Pb, Sn or mixed occupancy of two metals) systems as shown in Figure 2 [31,45,46,47,48,49,50,51,52,53,54]. The M2P2S6 system has emerged as an important system due to their 2D layered crystal structure coupled with highly tunable chemical properties via mixing various metals within the crystal lattice [31,45,46,47,48,49,50,51,52,53,54]. KInP2S7 shows quasi-layered features as shown in Figure 2b. Using Fe2P2S6 as an example to present the structure of the M2P2S6 system, which is shown in Figure 2a,c. The Fe2P2S6 is constructed by neutral [Fe2P2S6] slabs, which are constructed by [FeS6] octahedron and [P2S6] motifs. Within the asymmetric unit cell of Fe2P2S6, there are two independent Fe atomic positions. With leaving one Fe atomic position vacant and replacing another Fe atomic position by In atoms, the neutral [Fe2P2S6] slabs were changed to [InP2S6]− slabs. The P-P homoatomic bonds are broken with incorporation of In atoms, which results in the oxidation states for P changing from 4+ to 5+. One additional sulfur atom is incorporated in to [InP2S6]− slabs to link [PS4] tetrahedra, which forms [InP2S7]- slabs. Please notice, each [InS6] octahedral was shifted along [010] direction about ¼ b distance. The negatively charged [InP2S6]− slabs are compensated by inserting K+ cations. The trivalent In atoms within KInP2S7 can be replaced by isovalent transition metals such as Cr3+ and V3+, which introduce potential magnetic application into this system.

3.3. Bonding Pictures of KInP2S7

The AIIIP2S7 (A = K, Rb, Cs; III = V, Cr, In) family crystallizes in acentric C2 (no. 5) space group. The basic building units for KInP2S7 are intrinsically distorted [PS4] tetrahedron and [InS6] octahedron. The P-S distances within [PS4] tetrahedra are 2.005–2.137 Å. The bonding picture studies shows the covalent bonding nature of P-S interactions (Figure 3a). There are obvious attractors located between the P and S atoms. The covalent P-S interactions exhibit strong bonding characters with −ICOHP of 5.738 eV/bond for 2.05 Å P-S interactions. (Figure 3b). The P-S interactions were revealed to play an important role for contributing to the optical properties of KInP2S7 (vide infra). The distorted [InS6] octahedron is shown in Figure 3c. The central In atom is surrounded by four In-S interactions of 2.58 Å and two elongated In-S interactions of 2.70 Å, namely a 4 + 2 coordination environment. The two elongated 2.70 Å In-S interactions are located at the axial position and equatorial position, respectively. The COHP calculation (Figure 3b) and ELF (Figure S2) calculation indicated strong ionic interaction nature of In-S interactions. The calculated –ICOHPs for 2.58 Å In-S interactions and 2.70 Å In-S interactions are 1.939 eV/bond and 1.355 eV/bond, respectively. The distorted [InS6] octahedron contribute less than that of distorted [PS4] tetrahedron to the total optical properties of KInP2S7 (vide infra).

3.4. Magnetic Properties of KCrP2S7

The layered crystal structure coupled with flexible chemical properties of the AIIIP2S7 (A = K, Rb, Cs; III = V, Cr, In) family indicate the potential broad applications such as magnetic properties and optical applications and the interface between them. Hence, we measured the magnetic properties of high quality KCrP2S7 crystals (Figure 1 inset). Figure 4a shows the zero-field cooling (ZFC) and field cooling (FC) temperature dependene of the magnetic susceptibility of a KCrP2S7 single crystal measured under a magnetic field of 1 T employed within the ab plane. A clear peak is observed at 21 K, which should be attribute to an antiferromagnetic transition because of the overlaping of the ZFC and FC data and a neagtive Weiss temperature of −50 K from fitting the data to the modied Curie-Weiss law (Figure 4a). The antiferromagnetic state is also consistent with the linear field dependence in the low field region of the isothermal magnetization, as shown in Figure 4b. At T = 2 K, a metamagnetic spin-flop transtion is observed around 3 T, which is suppressed up on increasing temeprature and disappears above the magnetic ordering temeprature (Figure 4b). Such spin-flop transition is not observed under an out-of-plane magnetic field. (Figure 4b, inset). These observations agree well with the antiferromagnetic ground state with an inplane easy axis of the Cr3+ moment. Similar scenario has also been observed in other layered magnetic materials such as NiPS3 [55]. The effective magnetic moment µeff estimated from the Curie constant of the fits are 3.80 µB, which agrees well with the theoretical values of trivalent Cr3+ (3.87 µB). A previous study of KCrP2S7 crystals grown by KBr also found an antiferromagnetic transition at 17 K [37]. The calculated µeff with employing H//c* is 3.95 µB [37]. In this work, high quality crystals were grown by solid state chemistry method, which eliminated the possibility of incorporation of foreign elements. The trivalent M3+ is also supported by the electron-precise nature of KInP2S7, where In is also trivalent (vide infra).

3.5. Electronic Structures of KInP2S7

Since the trivalent nature of III metals are within the AIIIP2S7 (A = K, Rb, Cs; III = V, Cr, In) family, the charge-balanced formula (A+)(III3+)(P5+)2(S2−)7 can be established by assigning a formal charge of 1+ to the alkali metals, 5+ to the P atoms, and 2− to the sulfur atoms. The charge-balanced nature of KInP2S7 was verified by TB-LMTO-ASA calculations (Figure 5) and UV-Vis measurements (vide infra). KInP2S7 is predicated to be an indirect bandgap semiconductor with the top of valance band and the bottom of conduction band located at the A points and the Λ points, respectively. The energy gap separating the conduction band and the valence band is 2.38 eV, which is comparable to the experimentally measured value of 2.4(1) eV (vide infra). The top of the valance band is mainly contributed by S 3p orbitals (Figure 5b) together with very small contribution from the In 5s and 5p orbitals. There is no accountable contribution from P 3p orbitals and K 4s orbitals at the bottom of the top of valence band. The S 3p orbitals and the P 3p orbitals significantly contribute to the bottom of the conduction band, where very small amounts are contributed are from the In 5s and 5p orbitals and K 4s orbitals. Hence, we can anticipate that the optical properties of KInP2S7 are mainly contributed by [PS4] tetrahedra units coupled with certain contribution from the [InS6] octahedra.

3.6. Linear and Nonlinear Optical Properties of KInP2S7

KCrP2S7 is estimated to have a very small bandgap with the black appearance of the crystals. Hence, the optical properties were mainly carried on KInP2S7. The bandgap of KInP2S7 was estimated by UV-Vis measurements. The experimentally measured value is 2.4(1) eV (Figures S3 and S4), which agrees well with our theory study of 2.38 eV. KInP2S7 was predicated by L. Kang et al. to possess moderate SHG effects (18 × KDP) [2]. Our experiments verified this predication as shown in Figure S5. KInP2S7 does not exhibit type-I phase-matching behavior, where the SHG intensity increases first then decreases with particle size increasing. For KInP2S7 sample of particle size of 100 µm, the SHG intensity of KInP2S7 is about 0.51 × AgGaS2. Notice that, the quality of crystals may affect the SHG response [45]. KInP2S7 exhibited impressively high LDT of 5.2 × AgGaS2 (Table S1), which may originate from its high bandgap. More study is required to understand the high LDT of KInP2S7., The optical properties of KInP2S7 are dominantly contributed by [PS4] tetrahedra. Hence, a future bandgap engineering possibility is to modify the [PS4] tetrahedron, in example, by introducing As atoms or Sb atoms to replace P atoms so to suppress the bandgap and enhance SHG response [56]. To further understand the optical properties of KInP2P7, a DFT calculation is undergoing [57,58,59].

4. Conclusions

Two structurally known thiophosphates, KInP2S7 and KCrP2S7, were revisited in this work. Single phases and crystals of KInP2S7 and KCrP2S7 were grown by high temperature solid state reactions. KCrP2S7 is isostructural to KInP2S7, which features a layered structure. KInP2S7 and KCrP2S7 possess a close relationship to the layered thiophosphate M2P2S6, where the divalent metals within M2P2S6 are replaced by In3+ or Cr3+ and break down the P-P interactions. The K cations were inserted between [MP2S7]−M = Cr or In to compensate the charge and fill the space. Magnetic measurement on mm-sized crystals of KCrP2S7 verified the antiferromagnetic transition around 21K and the trivalent nature of Cr atoms. The bonding pictures of KInP2S7 were studied by ELF coupled with COHP calculations. The intrinsically distorted [PS4] tetrahedra and [InS6] octahedra are made by strong covalent P-S interactions and ionic In-S interactions, respectively. KInP2S7 is predicated to be an indirect bandgap semiconductor of 2.38 eV, which is confirmed by the UV-Vis measurement of 2.4(1) eV. Electronic structure analysis confirmed that the main contributing factor to the optical properties of KInP2S7 are [PS4] tetrahedra while small amounts of contribution are from [InS6] octahedra. KInP2S7 is not a type-I phase-matching materials and exhibits moderate SHG response (0.51 × AgGaS2, sample of particle size of 100 µm). The LDT of KInP2S7 is very high at 5.2 × AgGaS2. Bandgap engineering were undergone to enhance the SHG response of KInP2S7.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/cryst12111505/s1, Room temperature powder X-ray diffraction data (Figure S1), ELF calculation (Figure S2), UV-Vis data (Figure S3), Tauc plots (Figure S4), SHG measurements (Figure S5), LDT measurement results (Table S1).

Author Contributions

C.C. and V.N.: Methodology, Validation; S.K.C. and J.H.: Resources and Investigation; S.G.: Resources; J.W.: Data curation, Formal analysis, Funding acquisition, Supervision, Writing—original draft, Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by NASA’s support and award number No. 80NSSC22M0028. Work at the University of Arkansas (magnetic property study) is supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences program under Grant No. DE-SC0022006.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

J.W. would like to thank Kui Wu at Hebei University for helping on LDT measurement.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Powder X-ray diffraction results of KCrP2S7, the insert shows the optical microscope photo of selected KCrP2S7 crystals. The crystals were manually cut and selected for properties measurements.
Figure 1. Powder X-ray diffraction results of KCrP2S7, the insert shows the optical microscope photo of selected KCrP2S7 crystals. The crystals were manually cut and selected for properties measurements.
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Figure 2. (a) Ball-stick structure of Fe2P2S6 viewed along [010] direction, (b) ball-stick structure of KInP2S7 viewed along [100] direction, (c) a detailed view of [FeP2S3] layers within Fe2P2S6 viewed along [101] direction, (d) a detailed view of [InP2S7]− layer within KInP2S7 viewed along [101] direction. Fe: orange, P: black, S: yellow, K: green, In: pink.
Figure 2. (a) Ball-stick structure of Fe2P2S6 viewed along [010] direction, (b) ball-stick structure of KInP2S7 viewed along [100] direction, (c) a detailed view of [FeP2S3] layers within Fe2P2S6 viewed along [101] direction, (d) a detailed view of [InP2S7]− layer within KInP2S7 viewed along [101] direction. Fe: orange, P: black, S: yellow, K: green, In: pink.
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Figure 3. (a) 3D isosurfaces of the ELF for a [PS4] tetrahedral within KInP2S7 with η = 0.75, P: gray, S: yellow. (b) COHP analyses of selected interactions within KInP2S7. (c) The [InS6] octahedron with bond distances labeled. P: gray, In: pink, S: yellow.
Figure 3. (a) 3D isosurfaces of the ELF for a [PS4] tetrahedral within KInP2S7 with η = 0.75, P: gray, S: yellow. (b) COHP analyses of selected interactions within KInP2S7. (c) The [InS6] octahedron with bond distances labeled. P: gray, In: pink, S: yellow.
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Figure 4. (a) Temperature dependence of dc magnetic susceptibility of selected KCrP2S7 crystals measured in a field of 1 T employed parallel to the ab plane (H//ab). The red solid lines indicate the fit to the modified Curie-Weiss law. (b) Field dependence of isothermal magnetization (M) of KCrP2S7 at different temperatures, measured under H//ab. Inset: isothermal magnetization at 5 K with both in-plane (H//ab) and out-of-plane magnetic fields.
Figure 4. (a) Temperature dependence of dc magnetic susceptibility of selected KCrP2S7 crystals measured in a field of 1 T employed parallel to the ab plane (H//ab). The red solid lines indicate the fit to the modified Curie-Weiss law. (b) Field dependence of isothermal magnetization (M) of KCrP2S7 at different temperatures, measured under H//ab. Inset: isothermal magnetization at 5 K with both in-plane (H//ab) and out-of-plane magnetic fields.
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Figure 5. (a) Calculated band structure and (b) DOS of KInP2S7.
Figure 5. (a) Calculated band structure and (b) DOS of KInP2S7.
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Cropek, C.; Nguyen, V.; Chhetri, S.K.; Hu, J.; Guo, S.; Wang, J. Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7. Crystals 2022, 12, 1505. https://doi.org/10.3390/cryst12111505

AMA Style

Cropek C, Nguyen V, Chhetri SK, Hu J, Guo S, Wang J. Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7. Crystals. 2022; 12(11):1505. https://doi.org/10.3390/cryst12111505

Chicago/Turabian Style

Cropek, Craig, Vivian Nguyen, Santosh Karki Chhetri, Jin Hu, Shengping Guo, and Jian Wang. 2022. "Synthesis, Crystal and Electronic Structures, Nonlinear Optical Properties, and Magnetic Properties of Two Thiophosphates: KInP2S7 and KCrP2S7" Crystals 12, no. 11: 1505. https://doi.org/10.3390/cryst12111505

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