PHASE FORMATION IN THE FeSb2S4-FeLn2S4 SYSTEM, SYNTHESIS AND PROPERTIES OF COMPOUNDS OF THE FeLnSbS4 (Ln=Nd, Er) TYPE Текст научной статьи по специальности «Химические науки»

CHEMICAL PROBLEMS 2024 no. 3 (22) ISSN 2221-8688

361

UDC 546.722.863.22-722.65.22

PHASE FORMATION IN THE FeSb2S4-FeLn2S4 SYSTEM, SYNTHESIS AND PROPERTIES OF COMPOUNDS OF THE FeLnSbS4 (Ln=Nd, Er) TYPE

O.M. Aliev1, D.S. Azhdarova1, V.M. Ragimova1, T.F. Maksudova1, L.M. Gurbanova2

institute of Catalysis and Inorganic Chemistry named after M. Nagiyev, Baku, Azerbaijan 2Western Caspian University, Baku, Azerbaijan e-mail: aliyevimir@rambler.ru

Received 06.03.2024 Accepted 23.05.2024

Abstract: Phase formation in the FeSb2S4-FeNd2S4 and FeSb2S4-FeEr2S4 systems were studied by means of differential thermal analysis, X-ray diffraction technique, microstructural analysis and microhardness measurement. Phase diagrams of the title systems have been constructed and the formation of a quaternary sulfosalt with the FeLnSbS4 composition has been established. The compounds FeNdSbS4 and FeErSbS4 melt congruently at 960 and 1330 K, respectively, and form continuous substitutional solid solutions with FeSb2S4. Sulfosalts FeLnSbS4 crystallize in the orthorhombic structure with following unit cell parameters: a=11.392, b=14.132, c=3.746A, sp.gr. Pbam, z=4, density p=4.88 g/cm3 (for FeNdSbS4); a=11.360, b=13.842, c=3.600 A, sp. gr. Pbam z=4, p=5.17 g/cm3 (for FeErSbS4). The FeLnSbS4 type sulfosalts is classified under the FeSb2S4 berthierite structure.

Key words: system, phase diagram, sulfosalt, solid solutions, unit cell parameters, berthierite DOI: 10.32737/2221-8688-2024-3-361-368

Introduction

Obtaining and studying the fundamental physical properties of crystals with valuable, practically important characteristics is one of the main problems of modern science. The production of synthetic crystals largely determines the development of such important fields of technology as radio electronics, semiconductor and quantum electronics, technical optics, acoustics, etc. [1-5].

Here we study phase equilibria in the FeSb2S4-FeNd2S4 and FeSb2S4-FeEr2S4 quasiternary systems. The initial ternary sulphides are formed in the systems FeS - Sb2S3 and FeS - Ln2S3 (Ln = Nd, Er) quasibinary systems and have been studied in detail in the literature [6, 8]. The compounds FeNd2S4 and FeEr2S4 melt congruently and crystallize in the hexagonal syngony [1, 8].

The FeSb2S4 compound occurs in nature in the form of the mineral berthierite [9], and crystallizes in the orthorhombic structure with lattice parameters a = 11.44, b = 14.12, c = 4.76

A, z = 4, Sp. gr. Pbam. In the structure of FeSb2S4, there are two different kinds of Sb atoms, and each one is close to a sulfur atom (Sb - S distance = 2.5 A). The Fe atoms are surrounded by six sulfur atoms in a distorted octahedron; octahedra have common edges and form chains parallel to the "c" axis [9]. It should be mentioned that garavellite, or FeSbBiS4, is a naturally occurring mineral. A structural study of garavellite has not been carried out, but it has been determined that it crystallizes in the orthorhombic lattice with parameters: a = 11.439, b = 14.093, c = 3.754 A, z = 4; Sp. gr. Pbam [10]. This compound can be represented as the replacement of one antimony atom with a bismuth atom in the structure of berthierite FeSb2S4.

Complex compounds of rare earth elements and solid solutions based on them draw attention as magnetic, luminescent, acousto-optical, and other materials and employed in contemporary microelectronics

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CHEMICAL PROBLEMS 2024 no. 3 (22)

[11-16]. Previously, we [17-19] studied synthetic analogues of the berthierite mineral FeSb2S4 with "light" lanthanides.

The purpose of this work is to study phase

formation in the FeSb2S4 - FeNd2S4 (FeEr2S4) systems and obtain single crystals of compounds of the FeLnSbS4 (Ln=Nd, Er) type for physical measurements.

Experimental part

Quaternary alloys (FeSb2S4)1-x(FeLn2S4)x were obtained by fusing the original ternary compounds. Triple sulfides FeSb2S4 and FeLn2S4 (Ln=Nd, Er) were synthesized by the ampoule method from highly pure elements (iron carbonyl, antimony grade Su-3, lanthanide grade LnM-O and sulfur grade B5). The synthesis of compounds (FeSb2S4, FeNd2S4 and FeEr2S4) was carried out in evacuated 10-2 Pa quartz ampoules at a temperature of 1100-1150 K. Then, homogenizing annealing of samples was carried out at 950 K for 2 weeks synthesis. Obtained compounds were used in the production of quaternary alloys.

Quaternary alloys of the FeSb2S4-FeNd2S4 and FeSb2S4-FeEr2S4 systems were synthesized in single-section furnaces at 1250-1275 K. After holding (1 hour) at this temperature, the furnace was cooled to 650 K with a rate of 50o/hour, and

homogenizing annealing was carried out in this mode for 470-480 hours. Details of the synthesis procedure are given in [20].

The alloys were studied by differential-thermal analysis (DTA) in NTR-73 device (heating rate was 10o/min, alumel-chromium thermocouple is used, Al2O3 served as the standard) and X-ray diffraction technique (XRD) in D2 PHASER diffractometer from Bruker with CuKa radiation and Ni-filter, as well as microhardness and density measurement (in PMT-3 device). The melting point of the samples was determined with an accuracy of ±5 K, and the lattice parameters were calculated with an accuracy of ±0.001 A. The electrical properties of the obtained sulfosalts were carried out by the compensation method using a direct current probe described in [20].

Results and its discussion

Phase diagrams of the FeSb2S4-FeNd2S4 and FeSb2S4-FeEr2S4 systems, constructed according to DTA, X-ray diffraction data, microhardness and density measurements are presented in Fig. 1. (a; b). As can be seen, a complex interaction occurs between the initial components with the formation of the intermediate phase FeLnSbS4 (Ln=Nd, Er) and solid solutions based on FeSb2S4. Quaternary compounds FeNdSbS4 and FeErSbS4 melt congruently at 960 and 1330 K, respectively, and divide each system into two subsystems: FeSb2S4 - FeNdSbS4 and FeNdSbS4 - FeNd2S4 (FeSb2S4 - FeErSbS4 and FeErSbS4 - FeE^).

As can be seen, in both cases, FeSb2S4 and quaternary compounds (FeNdSbS4 and FeErSbS4) completely dissolve in each other at any ratio, both in liquid and solid states.

The presence of a continuous series of solid solutions in the corresponding subsystems was confirmed by the X-ray method. Fig. 2

shows X-ray diffraction patterns of the compounds FeNdSbS4 and FeErSbS4, and Table. 1 listed X-ray diffraction patterns data of quaternary and initial sulfosalts for comparison. The compounds FeNdSbS4 and FeErSbS4 are isostructural with FeSb2S4, crystallize in the orthorhombic system with the following unit cell parameters for FeNdSbS4: a=11.392, è=14.132, c=3.76 Â, V=603.566 Â, z=4, Sp. gr. Pbam p=4,88 g/cm3; and for FeErSbS4: a=11.360, b=13.842, c=3.600 Â, z=4, Sp. gr. Pbam, p=5.17 g/cm3.

The state diagram of the FeSb2S4-FeNdSbS4 system corresponds to the first type according to Rosebohm, i.e. the liquidus temperature constantly increases from a low-melting (FeSb2S4) to a high-melting component. Unlike the first subsystem, the state diagram of the FeSb2S4-FeErSbS4 subsystem belongs to the third type according to Rosebohm.

Fig. 1. Phase diagrams of the FeSb2S4-FeNd2S4 (a) and FeSb2S4-FeEr2S4 (b) systems

10 20 30 40 50 60

26

I

1000

2 0

Fig.2. Diffraction patterns of the FeErSbS4 (1) and FeNdSbS4 (2) compounds

Table 1. Interplanar distances and line intensities for the FeSb2S4, FeNdSbS4, _FeErSbS4, FeNd2S4 and FeEr2S4 compounds_

FeSb2S4 FeNdSbS4 FeErSbS4 FeNd 2S4, FeEr2S4

dexp I/Io dexp I/Io dexp I/Io dexp I/Io Dexp I/Io

4.300 80 6.018 10 5.910 5 8.201 5 2.916 20

3.620 90 4.362 25 5.676 8 7.053 8 5.007 10

3.350 60 3.687 30 4.617 10 6.904 45 3.992 100

3.150 90 3.613 60 4.389 15 6.514 5 3.513 50

3.010 60 3.534 40 4.272 15 5.802 10 3.201 5

2.830 90 3.432 25 3.652 25 5.593 10 3.142 5

2.600 100 3.189 50 3.460 35 4.471 10 2.629 25

2.510 60 3.079 30 3.330 10 5.196 40 2.377 70

3.230 40 3.022 40 3.312 8 7.784 10 2.314 40

2.155 60 2.963 20 3.070 35 4.600 100 2.262 10

2.035 60 2.849 100 2.967 30 4.487 15 2.199 20

1.990 70 2.747 35 2.950 25 4.268 10 2.051 20

1.900 60 2.644 60 2.925 12 4.100 100 1.993 5

1.870 90 2.614 70 2.840 100 3.930 10 1.969 10

1.785 60 2.539 10 2.688 30 3.692 5 1.920 15

1.760 60 2.501 20 2.625 50 3.573 10 1.855 10

1.690 40 2.309 10 2.540 80 3.525 5 1.761 5

1.660 40 2.222 30 2.437 10 4.493 5 1.744 15

1.630 5 2.131 10 2.266 10 4.463 10 1.681 5

1.585 60 1.973 5 2.191 30 3.276 5 1.647 10

1.495 20 1.929 35 2.080 8 3.734 20 1.580 10

1.415 40 1.873 30 1.914 8 2.680 15 1.553 5

1.365 40 1.821 5 1.900 40 2.579 14 1.534 10

1.335 30 1.807 15 1.800 35 2.343 15 1.492 15

1.318 20 1.718 20 1.791 8 2.075 8 1.463 5

1.255 30 1.669 5 1.740 5 2.050 10

1.079 70 1.655 10 1.972 5

1.059 70 1.618 5 1.866 10

1.045 50 1.475 10

Table 2. Parameters of crystal lattices of solid solutions (FeSb2S4 )1-x(FeNdSbS4)x

Composition Parameters of the elementary cell, Â Melting point, K P, g/cm3 HH, MPa

a b c

FeSb2S4 11.44 14.10 3.76 1030 4.65 1450

FeSbi.9Nd0.iS4 11.438 14.10 3.758 770-1020 4.69 1600

FeSb1.sNd0.2S4 11.432 14.098 3.754 920-1005 4.73 1730

FeSb17Nd03S4 11.430 14.095 3.752 930-980 4.75 1830

FeSb1.6Nd0.4S4 11.427 14.094 3.750 945-970 4.80 1900

FeNdSbS4 11.392 14.132 3.746 960 4.88 1900

Fig. 3. Dependence of microhardness (a) and density (b) of solid solutions (FeSb2S4)1-x(FeNdSbS4)x on composition.

Solid solutions (FeSb2S4)1-x(FeNdSbS4)x and (FeSb2S4)1-x(FeErSbS4)x crystallize in the orthorhombic system and belong to the substitution type. The lattice parameters of solid solutions vary linearly with composition change (Vegard's law), which also proves the formation of continuous solid solutions (see Table 2). In the FeSb2S4-FeNdSbS4 and FeSb2S4-FeErSbS4 systems, the occurrence of continuous solid solutions was also established by measuring microhardness and density depending on the composition (Fig. 3). As can be seen, the curves of microhardness and pycnometric density of solid solutions (FeSb2S4)1-x(FeNdSbS4)x vs.

composition pass through a maximum.

The temperature dependence of the electrical conductivity (Fig. 4, a) and thermo-emf of the FeNdSbS4 and FeErSbS4 quaternary sulfosalts was measured in the 293-900 K temperature range (Fig. 4, b). As can be seen, the inflection in the temperature dependence of electrical conductivity at 400-500 K corresponds to the region of impurity conductivity. With increasing temperature at 550-560 K the intrinsic conductivity appears. The band gap calculated from the intrinsic conductivity region is AE=1.36 and AE=1.45 eV for FeNdSbS4 and FeErSbS4, respectively.

Fig. 4. Temperature dependence of electrical conductivity (a) and thermo-emf (b) on the composition for the FeNdSbS4 (1) and FeErSbS4 (2) compounds

The thermo-emf coefficient from room temperature to the temperature of transition to intrinsic conductivity increases, and in its own region it naturally decreases. The temperature change in the thermo-emf coefficient is in good

agreement with the change in the electrical conductivity of these compounds. In the two-phase model, thermo-emf is expressed by the formula:

a =

hp,

P:

where ap1 and ap2 are thermo-emfs arising from the presence of light and heavy holes, respectively. If the electrical conductivity of heavy holes is small compared to the electrical conductivity of light holes, then the value of p2 in the denominator can be neglected. If

(1)

approximately equal to the thermo-emf of light holes. In the case of a simple parabolic band structure and a power-law dependence of the mean free path on energy, the expression for thermo-emf at an arbitrary degree of degeneracy has the form:

Op2P2« OpiPi then the total

thermo-emf is

k r (r + 2) F) " e (r + 2) F (n )

(2)

2

F (Л ) = J

0 x2dx

ex -Л+1

(3)

In the case of a non-degenerate electron gas, expression (2) is simplified:

k

a = —

e

r + 2+lg

2(2 TonKT) ' Jfn

(4)

where m is the effective mass of the density of states:

3/ y

m=n )

where N is the number of ellipsoids; mi, m2, m3 principal value of the effective mass tensor, n-reduced chemical potential.

Thus, the FeSb2S4-FeLn2S4 (Ln=Nd, Er) systems have been studied and their phase diagrams have been constructed. The formation of quaternary FeNdSbS4 and FeErSbS4 compounds with melting points 960 and 1330 K, respectively, has been established. It was

shown that FeLnSbS4 divides the FeSb2S4-FeLn2S4 system into two FeSb2S4-FeLnSbS4 and FeLnSbS4-FeLn2S4 subsystems. In the first subsystem, continuous solid solutions are formed, and the second subsystem is of the eutectic type. Coordinates of eutectic points: 30 mol% FeSb2S4 and 650 K (for the FeSb2S4-FeNd2S4) 35 mol% FeSb2S4 and 1130K (for the FeSb2S4-FeEr2S4).

0

2

Conclusion

Phase equilibria in the FeSb2S4-FeNd2S4 and FeSb2S4-FeEr2S4 systems were studied by physicochemical methods of analysis: differential thermal analysis, X-ray diffraction technique, microstructural analysis, as well as measurements of density and microhardness. The hase diagrams of the studied quasibinary systems were constructed. It has been established that in these systems sulfosalts FeNdSbS4 and FeErSbS4 are formed and melt congruently at 960 and 1330 K, respectively.

These compounds form solid solutions of the substitution type in a wide range with FeSb2S4. Lanthanide-containing sulfosalts crystallize in the orthorhombic system.

The temperature dependences of electrical conductivity and thermo-EMF of quaternary sulfosalts FeNdSbS4 and FeErSbS4 in the temperature range 230-900 K have been studied. The band gap calculated from the intrinsic conductivity region is AE=1.36 and AE=1.45 eV for FeNdSbS4 and FeErSbS4, respectively.

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FeSb2S4 - FeLn2S4 SÎSTEMÎNDÔ FAZA9M9L9G9LM9, FeLnSbS4 (Ln=Nd, Er) TiPLi BÎRL9ÇM9L9RÎN SiNTEZi УЭ XASSÔLÔRÎ

Ö.M. aiiyev1, D.S. ajdarova1, V.M. Rahimova1, T.F. Maqsudova1, L.M. Qurbanova2

1AR ETN akad. M. Nagiyev adina Kataliz va Qeyri-üzvi kimya institutu, Baki, Azarbaycan

2Xaz3r Universiteti, Baki, Azarbaycan e-mail: aliyevimir@rambler.ru

Xülasa: FeSb2S4 - FeNd2S4 и FeSb2S4 - FeEr2S4 sistemlarinda fazaamalagalma diferensial-termiki, rentgenfaza, mikroquruluç va mikrobarklik analiz metodlari vasitasila tadqiq edilarak, FeLnSbS4 tarkibli dördlü sulfoduzun alinmasi müayyan edilmiçdir. FeNdSbS4 va FeErSbS4 birlaçmalari uygun olaraq 960 va 1330 K temperaturda ariyir va FeSb2S4 ila avazolunan tipli bark mahlullar amala gatirir. FeLnSbS4 tipli sulfoduzlar rombik sinqoniyada kristallaçir, elementar qafas parametrlari:

FeNdSbS4 -а=11,392, ¿=14,132, c=3,746Á, faza qr. Pbam, z=4, sixliq p=4,88 q/sm3, FeErSbS4 -а=11,360, ¿=13,842, с=3,600 Á, faza qr. Pbam, z=4, p=5,17 q/sm3-dir. FeLnSbS4 tipli sulfoduzlar berterit qurulu§lu FeSb2S4 tipina aiddir.

A?ar sozlar: sistem, faza diaqrami, sulfoduz, bark mahlul, elementar qafas parametrlari, berterit

ФАЗООБРАЗОВАНИЕ В СИСТЕМЕ FeSbiS4 - FeL^ , СИНТЕЗ И СВОЙСТВА СОЕДИНЕНИЙ ТИПА FeLnSbS4 (Ln=Nd, Er)

О.М. Алиев1, Д.С. Аждарова1, В.М. Рагимова1, Т.Ф. Максудова1, Л.М. Гурбанова2

1 Институт Катализа и Неорганической Химии им. акад. М. Нагиева, МНО АР, Баку, Азербайджан 2Западно-Каспийский Университет, Баку, Азербайджан e-mail: aliyevimir@rambler.ru

Резюме: Фазообразование в системах FeSb2S4 - FeNd2S4 и FeSb2S4 - FeEr2S4 были

изучены методами дифференциально-термического, рентгенофазового, микроструктурного анализа и измерением микротвердости. Впервые построены диаграммы состояния этих систем и установлено образование четверных сульфосолей FeNdSbS4 и FeErSbS4, плавящихся конгруэнтно при 960 и 1330К, соответственно. Эти соединения образуют с FeSb2S4 непрерывные области твердых растворов типа замещения. Сульфосоли FeLnSbS4 кристаллизуются в ромбической сингонии с параметрами элементарный ячейки: FeNdSbS4-а=11,392, ¿=14,132, с=3,746 Á, пр.гр. Pbam, z=4, плотность р=4,88 г/см3, FeErSbS4-o=11,360, ¿=13,842, с=3,600 Á, пр.гр. Pbam, z=4, р=5,17 г/см3. Сульфосоли типа FeLnSbS4 относятся к структурному типу бертьерита FeSb2S4.

Ключевые слова: система, фазовая диаграмма, сульфосоль, твердые растворы, параметры элементарной ячейки, бертьерит.