Physical properties of layer-type MPS3 compounds: M0.5In0.33PS3 (M=Cd, Fe, Mn)

Journal of Alloys and Compounds 329 (2001) 92–96

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Physical properties of layer-type MPS 3 compounds: M 0.5 In 0.33 PS 3 (M5Cd, Fe, Mn) a, *, P. Barahona a , O. Pena ˜ b , M. Mouallem-Bahout b , R.E. Avila c ´ V. Manrıquez b

a ´ , Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile Departamento de Quımica ´ , UMR 6511, CNRS-Universite´ de Rennes I, Institut de Chimie de Rennes, 35042 Rennes Cedex, Chimie du Solide et Inorganique Moleculaire France c ´ y Desarrollo, Comision ´ Chilena de Energıa ´ Nuclear, Casilla 188 -D, Santiago, Chile Departamento de Investigacion

Received 23 March 2001; accepted 2 May 2001

Abstract Cd 0.5 In 0.33 PS 3 , Fe 0.5 In 0.33 PS 3 , Mn 0.5 In 0.33 PS 3 , and compounds have been synthesized by ceramic method at 923 K. These compounds were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential thermal and thermogravimetric analyses (DTA / TG), energy dispersive X-ray (EDX), magnetic susceptibility measurements and electrochemical impedance spectroscopy. The antiferromagnetic interactions present in the phases MPS 3 , are attenuated in the mixed phases M 0.5 In 0.33 PS 3 . This is explained by the larger separation of the ions M 21 in the mixed phase and therefore by a decrease of the magnetic interaction. The limit phase FePS 3 is the more conductive one among the MPS 3 compounds. This tendency is maintained in the studied mixed phases. Thus, the phase Fe 0.5 In 0.33 PS 3 shows an electrical conductivity of s 53.0310 28 S / cm at room temperature.  2001 Elsevier Science B.V. All rights reserved. Keywords: Chalcogenophosphates; Layered compounds; Magnetic properties

1. Introduction The study of layered transition-metal phosphorous trichalcogenides MPS 3 has become the subject of an impressive field of research in solid state physics and chemistry. Layer compounds containing (P2 X 6 )42 anions (X5S or Se) linked together by metal cations constitute a large family of solids with exhibit a variety of interesting physical behaviours. The investigations of the physical properties have been stimulated because they present good optical properties useful for photoelectrical applications. Furthermore, their ability to intercalate lithium reversibly, either chemically or electrochemically, make them promising electrode materials for Li-based reversible high-density batteries [1–3]. In the layers of these materials, the metal transition cations M 21 and the P–P pairs occupy the octahedral holes defined by the chalcogen framework. The formation of vacant octahedral sites into a layer yields another variation

*Corresponding author. Tel.: 156-2-6787-267; fax: 156-2-2713-888. ´ E-mail address: [email protected] (V. Manrıquez).

to the layered chalcogenophosphate structure; such as in the case of In III 2 / 3 PS 3 [4] . Due to the fact that the structure of MPS 3 remains the same for various M 21 ions, the MPS 3 series offers an opportunity to study the controlled variation of the physico-chemical properties of these systems by homocharge or heterocharge substitution of the M 21 ions by different metal ions. By substituting the divalent M ion in layered M 2 P2 S 6 (M5Cd, Fe, Mn) phases such as I III II II I II A B P2 S 6 (1,3), A B P2 S 6 (2,2) and A B P2 S 6 (1,2), with A5Ag, Cu, and B5V, Cr, In, Sc, can be obtained [5–7]. The study of cation-mixed chalcogenophosphate phases gives appreciable information on the basic properties and their trends in these layered materials, the mixing of the cations being responsible for a chemical disorder, which can cause a significant modification of the physical properties. The reported mixed system Cd 12x Fe x PS 3 form a disordered solid solution, as far as the cationic distribution in the metal plane is concerned. As a result this disordered system exhibits interesting magnetic properties [8,9]. The present work reports the preparation, infrared spectra, conductivity and magnetic measurements of the

0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 01 )01602-4

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mixed-cation phases M 0.5 In 0.33 PS 3 (with M5Mn, Fe, Cd). The results are compared and discussed with respect to those for the end-member phases MPS 3 (M5Cd, Fe, Mn) and In 2 / 3 PS 3 . 2. Experimental

2.1. Synthesis of metal phosphorous trisulfides For the preparation of M 0.5 In 0.33 PS 3 phases (M5Mn, Cd, Fe), powders of the corresponding high purity (99.99%) element powders were mixed in stoichiometric amounts, sealed in evacuated quartz tubes, and then heated at 923 K for 2 weeks. After the reaction was completed, the reacted matter was slowly cooled to room temperature. Homogeneous and well crystalline materials were obtained after grinding and reheating.

2.2. Characterization The X-ray powder diffraction (XRD) data were collected at room temperature on a Siemens D 5000 powder diffractometer, with Cu Ka radiation in the range 5,2u , 90. The elemental analyses for all compounds were performed by EDX. SEM-EDX analyses were obtained on a Cameca SU 30 with detector Princeton Gamma. Differential thermal analysis (DTA) and thermogravimetric analysis (TG) were performed on an STA 1500H / 625 Thermal Analysis System (Rhoeometric Scientific). The DTA / TG curves were run simultaneously on each sample from room temperature to 1273 K, in flowing atmosphere of nitrogen at a heating rate of 10 K / min. Infrared spectra were recorded on a Bruker Vector 22 with a Fourier transformed SJ-IR spectrometer in the spectral range 250–600 cm 21 . The spectra of the powders were recorded in KBr pellets containing a small amount of the compound. The magnetic susceptibility ( x ) measurements were performed on polycrystalline samples between 2 K and room temperature under a constant field strength of 1 kG, using a SHE VTS-906 SQUID detection system. Electrical conductivity of the samples was measured by ac and dc methods on cylindrical disk samples, mounted between two gold electrodes. The ac conductivity measurements were carried out by an ac complex impedance analysis in the frequency range from 0.1 Hz to 10 MHz using a Solartron SI 1260 Impedance / Gain Phase Analyser with a signal level 0.2 to 1 V. Direct current (dc) conductivity was determined with a Keithley 237 sourcemeter.

Fig. 1. XRD patterns of (a) Cd 0.5 In 0.33 PS 3 , (b) Fe 0.5 In 0.33 PS 3 and (c) Mn 0.5 In 0.33 PS 3 with the corresponding limit phases.

homogeneity phases of the prepared samples. The mixed phases of Cd 0.5 In 0.33 PS 3 and Fe 0.5 In 0.33 PS 3 present reflections between those corresponding to the limit phases (Fig. 1). Elemental analyses were carried out on the studied samples (Table 1). Differential thermal and thermogravimetric analyses (DTA / TG) carried out under flow of nitrogen, indicated that the mixed phases are stable at ca. 6008C, while the limit phases are stable only up to temperatures ca. 5508C. Fig. 2 shows the infrared spectra (600–250 cm 21 ) for the limit phases CdPS 3 , In 2 / 3 PS 3 and mixed phase Cd 0.5 In 0.33 PS 3 . The band assignments are interpreted in terms of internal modes of PS 3 and by combining their in-phase and out-of-phase translational and rotational Table 1 Elemental analyses of the mixed phases M 0.5 In 0.33 PS 3 (M5Cd, Fe, Mn)

Calc % Found

Cd 0.5 In 0.33 PS 3 Cd 25.4 25.6

In 17.1 16.9

P 14.0 14.1

S 43.5 43.3

Calc% Found

Fe 0.5 In 0.33 PS 3 Fe 14.5 14.7

In 19.6 19.3

P 16.0 16.2

S 49.8 48.9

Calc% Found

Mn 0.5 In 0.33 PS 3 Mn In 14.4 19.7 14.8 19.0

P 16.1 16.3

S 50.0 49.6

3. Results and discussion The XRD of the mixed phases M 0.5 In 0.33 PS 3 (M5Cd, Fe, Mn) show sharp lines that reflect the crystallinity and

´ et al. / Journal of Alloys and Compounds 329 (2001) 92 – 96 V. Manrıquez

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Fig. 3. Impedance plot and Nyquist diagram for Fe 0.5 In 0.33 PS 3 .

Fig. 2. FTIR spectra of (a) CdPS 3 , (b) Cd 0.5 In 0.33 PS 3 and (c) In 2 / 3 PS 3 .

motions [10]. The spectra for the mixed phases show three bands splitting with respect to the limit phases MPS 3 . The corresponding band wavenumbers and appropriate assignments are reported in Table 2. The degenerate stretching band nd (PS 3 ) which occurs at 560 cm 21 in pure MPS 3 , is 21 split into three components at 590, 560 and 540 cm in the mixed phases. The symmetric PS 3 bending band d s (PS 3 ) at 300 cm 21 split into two bands at 320 and 310 cm 21 . The d d (PS 3 ) vibrations at 255 cm 21 split into three components at 290, 270 and 254 cm 21 . The medium infrared band at 450 cm 21 , corresponding to the T 9z (PS 3 ) or n(P–P) modes, is not affected in the mixed phase.

The IR spectra of the phase In 2 / 3 PS 3 present several bands due to the metal-deficient crystal structure with two families of P2 S 42 entities [4]. On the other hand, the mixed 6 phases show less bands than the limit phase In 2 / 3 PS 3 . The symmetric valence mode ns (PS 3 ) which occurs at 370 cm 21 in pure In 2 / 3 PS 3 remains unaffected in the mixed phase. This indicates that the mixed phases show increasing symmetry compared to the limit phase of indium. Both XRD and IR data can be explained by mixed phases M 0.5 In 0.33 PS 3 (M5Cd, Fe, Mn), where the cation M 21 is partially substituted by In 31 to form a defect crystal structure which retains the structure of MPS 3 (M5Cd, Fe, Mn). A preliminary investigation was carried out by ac impedance measurements on pellets of the limit and mixed phases, in the frequency range of 0.1 Hz to 10 MHz at room temperature, towards modelling the transport mechanisms through the material. Direct current (dc) measurements were performed, to ascertain the existence of slow

Table 2 Infrared band wavenumbers (cm 21 ) of MPS 3 and M 0.5 In 0.33 PS 3 phases in the solid state at room temperature (M5Cd, Fe, Mn) CdPS 3

FePS 3

MnPS 3

In 2 / 3 PS 3

Cd 0.5 In 0.33 PS 3

Fe 0.5 In 0.33 PS 3

Mn 0.5 In 0.33 PS 3

Approx. type of motions

562 s

572 s

572 s

595 583 565 551 536

590 w 561 s 542 w

600 w 562 s 541 w

590 w 570 s 545 w

nd (PS 3 )

448 w

444 w

448 w

451 m

449 m

445 m

449 m

371 w

372 vw

375 vw

371 vw

Comb. T 9z (PS 3 ) (n (P–P)) ns (PS 3 )

307 w

301 w

306 w

329 w 320 w 307 w

326 w 310 vw

323 vw 305 w

325 w 310 w

ds (PS 3 )

250 s

256 s

252 s

287 s 267 s 253 s

290 vw 277 vw 250 s

287 vw 278 vw 250 s

290 vw 277 vw 254 s

dd (PS 3 )

s sh vw vw vw

´ et al. / Journal of Alloys and Compounds 329 (2001) 92 – 96 V. Manrıquez Table 3 Conductivity values from dc measurements at room temperature Compounds

s (S cm 21 )

CdPS 3 FePS 3 MnPS 3 Cd 0.5 In 0.33 PS 3 Fe 0.5 In 0.33 PS 3 Mn 0.5 In 0.33 PS 3

,10 211 5.0310 26 9.2310 28 2.5310 210 3.0310 28 5.7310 211

relaxation mechanisms that may not be accessible through the impedance measurements. An overview of the room temperature behaviour was established for all samples. A single impedance arc was found for the phase Fe 0.5 In 0.33 PS 3 . On the contrary, Cd 0.5 In 0.33 PS 3 and Mn 0.5 In 0.33 PS 3 are very resistant and do not present Nyquist diagrams. The Nyquist diagram for Fe 0.5 In 0.33 PS 3 (Fig. 3) could be interpreted in terms of an equivalent circuit, such as the one represented in the same figure. The impedance arc should be associated with the intergranular transport mechanism [11]. Direct current (dc) measurements for all the phases are collected in Table 3.

95

The limit phase FePS 3 is the most conductive and this tendency is maintained in the mixed phases. Magnetic measurements were carried out on polycrystalline samples. The limit phases FePS 3 and MnPS 3 present an antiferromagnetic behaviour, CdPS 3 is diamagnetic, while the phase In 2 / 3 PS 3 presents an independent-temperature paramagnetism. The mixed phases Fe 0.5 In 0.33 PS 3 and Mn 0.5 In 0.33 PS 3 keep the antiferromagnetic behaviour of the parent compounds (Fig. 4), while the compound Cd 0.5 In 0.33 PS 3 remains diamagnetic. Table 4 shows the magnetic parameters, evaluated at T $1608C in the paramagnetic region, for the mixed phases and for the limit phases. The antiferromagnetic interactions present in MnPS 3 , characterized by a T N and a negative u value [12], are attenuated in the mixed phase Mn 0.5 In 0.33 PS 3 . This can be explained by a larger separation of the ions Mn 21 in the mixed phase and, therefore, a decrease of the interaction. The magnetic moments correspond to the spin-only moment ( meff 52[S(S11)] 1 / 2 ), in both compounds MnPS 3 and Mn 0.5 In 0.33 PS 3 . Our measurements of the magnetic susceptibility versus temperature carried out on FePS 3 show, in addition to the maximum at 121 K reported previously [13], the presence of another maximum at a temperature of 35 K, the previous measurements of Ref. [13] began only above 50 K. In the corresponding mixed phase Fe 0.5 In 0.33 PS 3 these two maxima are still observed, one at 40 K and another, less defined, at above 100 K. Here again, interactions are diminished, in the same way as in the phase Mn 0.5 In 0.33 PS 3 compared to MnPS 3 , due to a larger M–M distance as M (M5Mn, Fe) is substituted for indium. The magnetic moments for the phase FePS 3 and the mixed phase Fe 0.5 In 0.33 PS 3 show larger values than the spin-only value for a high spin Fe 21 ion (4.90 BM), which suggests a sizable spin–orbit contribution.

Acknowledgements

Fig. 4. Inverse magnetic susceptibility as a function of temperature for the cation-mixed Fe 0.5 In 0.33 PS 3 and Mn 0.5 In 0.33 PS 3 .

Research financed by grants FONDECYT No. 1990972, FONDECYT No. 2000001 and CNRS-CONICYT No. 10071.

Table 4 Experimental and calculated magnetic parameters for M 0.5 In 0.33 PS 3 , MPS 3 and In 2 / 3 PS 3 phases (M5Cd, Fe, Mn) Compounds

u (K)

Cd 0.5 In 0.33 PS 3 Fe 0.5 In 0.33 PS 3 Mn 0.5 In 0.33 PS 3 In 2 / 3 PS 3 CdPS 3 FePS 3 b MnPS 3

Temperature-independent diamagnetism, x300 K |20.7310 24 emu / mol 21.6 4.30 a 3.46 a 2126 4.16 a 4.19 a 24 Temperature-independent paramagnetism, x300 K |11.3310 emu / mol Temperature-independent diamagnetism, x300 K |20.8310 24 emu / mol 104 4.94 4.90 2241 6.03 5.92

a b

Calculated for 50% M133% In ions (mixed phases). From Ref. [14].

meff (BM / mol)

mth (BM)

T order (K) 40, 100 15

126 15, 110

96

´ et al. / Journal of Alloys and Compounds 329 (2001) 92 – 96 V. Manrıquez

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