The ternary system Tm2O3–SrO–CuO: compounds and phase relations

Journal of Alloys and Compounds 309 (2000) 95–99

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The ternary system Tm 2 O 3 –SrO–CuO: compounds and phase relations a, a a,b a a a C.Q. Han *, X.L. Chen , J.K. Liang , Q.L. Liu , Y. Chen , G.H. Rao a

Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Science, Beijing 100080, PR China b International Center for Materials Physics, Chinese Academy of Sciences, Shenyang 110015, PR China Received 19 April 2000; accepted 19 May 2000

Abstract The subsolidus phase relations of the Tm 2 O 3 –SrO–CuO ternary system have been investigated by X-ray powder diffraction. All samples were synthesized in air at 9508C. There is no ternary compound in the Tm 2 O 3 –SrO–CuO system at 9508C. The system can be divided into six three-phase regions. A new binary compound SrTm 2 O 4 is identified. This compound crystallizes in an orthorhombic unit ˚ b53.3771 A ˚ and c511.8173 A. ˚  2000 Elsevier Science S.A. All cell with space group Pnma and lattice constants of a510.0082 A, rights reserved. Keywords: Tm 2 O 3 –SrO–CuO; Crystal structure; Phase diagram

1. Introduction A series of R 2 O 3 –BaO–CuO (R, rare earth) ternary systems has been investigated to clarify the phase relations and to search for new superconductors. These ternary systems include La 2 O 3 –BaO–CuO [1,2], Y 2 O 3 –BaO– CuO [3–5], Gd 2 O 3 –BaO–CuO [6], Nd 2 O 3 –BaO–CuO [7], Ho 2 O 3 –BaO–CuO [8,9], Dy 2 O 3 –BaO–CuO [8], Yb 2 O 3 –BaO–CuO [10] and Pr 6 O 11 –BaO–CuO [11]. However, the ternary systems of R 2 O 3 –SrO–CuO has been less investigated. Only the La 2 O 3 –SrO–CuO system [12–14] and the Nd 2 O 3 –SrO–CuO system [15,16] have been reported. In order to find further new compounds, it is necessary to investigate the phase relations of other R 2 O 3 – SrO–CuO systems. As one of a series we report here the compounds and subsolidus phase relations of the Tm 2 O 3 – SrO–CuO ternary system. All samples were sintered at 9508C in air.

2. Experimental details

and CuO. The raw powders with proper compositions were thoroughly mixed, ground and pressed into pellets, which were sintered at about 9508C in air for about 48 h, and then slowly cooled in the furnace to room temperature. The above process was repeated for some of the samples until homogeneity was reached. However, we found that the samples rich in SrO were unstable and tended to deliquesce into SrO?2H 2 O in the air. This is consistent with the results reported by Liang and co-workers [17]. Thirtythree samples with different compositions were prepared and their compositions are shown in Fig. 1.

2.2. X-ray powder diffraction analysis Phase identification of the samples was carried out on a Rigaku Rint-2400 diffractometer with Cu Ka radiation and a graphite monochromator, operating at a step-scan mode with a scanning step of 2u 50.028 and a sampling time of 2 s. For the measurement of lattice parameters of the compounds, pure Si was added to the specimens as an internal standard.

2.1. Preparation of samples A series of Tm 2 O 3 –SrO–CuO samples of different composition were prepared by solid-state reaction of an appropriate mixture of high purity (.99.9%) Tm 2 O 3 , SrO *Corresponding author. E-mail address: [email protected] (C.Q. Han).

3. Results

3.1. Subsolidus phase relations According to the results of X-ray diffraction analysis, the subsolidus phase relations of the Tm 2 O 3 –SrO–CuO

0925-8388 / 00 / $ – see front matter  2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 00 )01041-0

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C.Q. Han et al. / Journal of Alloys and Compounds 309 (2000) 95 – 99

Fig. 1. The subsolidus phase relations of TmO 1.5 –SrO–CuO system derived from samples sintered at 9508C in the air: (d) single phase, (s) binary phases, (n) trinary phases.

system are shown in Fig. 1. There are six three-phase regions and no ternary compounds in Tm 2 O 3 –SrO–CuO system under the present experimental conditions.

˚ b53.46 A ˚ and c512.38 A. ˚ Our result is in a510.74 A, good agreement with the results previously reported [18].

3.1.1. Tm2 O3 –CuO system In the binary system Tm 2 O 3 –CuO, only one compound, Cu 2 Tm 2 O 5 , is identified. It crystallizes in an orthorhombic unit cell with space group Pna21 . Its lattice parameters are

3.1.2. SrO–CuO In the system pounds Sr 2 CuO 3 and Sr 14 Cu 24 O 41

system SrO–CuO at 9508C, four binary com[19,20], SrCuO 2 [20,21], SrCu 2 O 2 [22] [23] have been reported. The compound

Fig. 2. Rietveld refinement results of SrTm 2 O 4 : dots, raw data; solid curve, calculated profile. The curve at the bottom represents the difference between the observed and calculated profiles, the vertical bars indicate the peak positions.

C.Q. Han et al. / Journal of Alloys and Compounds 309 (2000) 95 – 99

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Table 1 ˚ b53.3771(1) A, ˚ c511.8173(1) A, ˚ space group Pnma, Z54 List of d spacings, diffraction intensity and hkl for SrTm 2 O 4 , a510.0082(1) A, No.

hkl

d calc

d obs

Icalc a

Iobs

No.

hkl

d calc

d obs

Icalc a

Iobs

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

002 102 200 202 011 111 004 302 104 112 210 211 204 212 113 311 402 213 114 313 214 410 411 015 502 206 215 306 020 116 600 414 512 216 008 024 108 322 604 224 416

5.909 5.088 5.004 3.819 3.247 3.091 2.955 2.906 2.834 2.815 2.801 2.725 2.545 2.531 2.485 2.328 2.304 2.283 2.172 2.034 2.033 2.011 1.983 1.937 1.896 1.833 1.807 1.696 1.690 1.678 1.668 1.663 1.654 1.611 1.478 1.467 1.462 1.461 1.453 1.408 1.407

5.91 5.09 5.01 3.818 3.250 3.087 2.953 2.905

2 11 14 5 5 3 48 100 4 85 40 3 3 2 13 6 3 2 7 5 37 25 4 2 3 7 2 16 16 18 11 23 17 6 3 11 3 25 12 2 4

3 12 15 7 6 5 51 100

42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82

317 118 218 516 712 522 226 326 418 508 620 810 2 0 10 518 028 1 1 10 608 128 624 132 230 716 902 814 2 1 10 234 430 4 1 10 718 136 528 434 532 906 10 1 0 2 2 10 1 1 12 3 2 10 628 922 10 1 4

1.376 1.342 1.307 1.297 1.286 1.262 1.242 1.197 1.191 1.189 1.187 1.173 1.150 1.122 1.112 1.109 1.106 1.106 1.102 1.100 1.099 1.095 1.093 1.091 1.089 1.030 1.027 1.019 0.983 0.973 0.972 0.970 0.969 0.969 0.960 0.951 0.942 0.930 0.926 0.918 0.913

1.3754 1.3409 1.3061 1.2959 1.2847 1.2605 1.2415 1.1964

2 3 4 4 8 2 4 10 4 2 7 2 2 2 2 2 2 2 10 5 2 5 5 3 2 4 3 3 3 3 3 5 3 3 3 3 4 2 4 8 4

3 4 5 5 7 3 4 8

a

2.813 2.798 2.723 2.543 2.528 2.483 2.326 2.303 2.281 2.170 2.032 2.010 1.981 1.935 1.895 1.832 1.806 1.696 1.688 1.677 1.667 1.662 1.653 1.610 1.4768 1.4655 1.4593 1.4520 1.4064

89 46 4 5 4 14 7 5 4 8 40 24 5 5 5 8 4 17 18 18 14 23 17 7 4 13 24 12 6

1.1865 1.1727 1.1498 1.1207 1.1115 1.1051 1.1007 1.0986 1.0939

1.0291 1.0264 1.0185 0.9826 0.9722 0.9695 0.9678 0.9590 0.9504 0.9410 0.9298 0.9249 0.9172 0.9122

7 3 3 3 4 5 8 7 6

4 4 4 3 5 5 5 4 3 3 3 3 5 3

Icalc ,2 are not listed.

SrCu 2 O 2 was prepared by firing SrO and CuO at 700– 8008C in air, but we did not synthesize this compound. Chen et al. [16] and De Leeuw et al. [14] reached the same conclusion. So only three of them, Sr 2 CuO 3 , SrCuO 2 and Sr 14 Cu 24 O 41 , have been detected in our investigation of the SrO–CuO phase diagram at 9508C. The compound Sr 2 CuO 3 belongs to an orthorhombic system with space group Immm. Its lattice parameters are ˚ b53.91–3.913 A ˚ and c53.48–3.50 A ˚ a512.68–12.71 A, [19,20]. The compound SrCuO 2 crystallizes in an ortho˚ rhombic lattice, space group Cmcm, with a53.562 A, ˚ and c53.918 A ˚ [20,21]. The compound b516.32 A Sr 14 Cu 24 O 41 has an orthorhombic lattice, space group ˚ b513.389 A ˚ Fmmm, with lattice parameters a511.466 A, ˚ [23]. and c53.918 A

3.1.3. Tm2 O3 –SrO system In the binary system Tm 2 O 3 –SrO, a new binary compound SrTm 2 O 4 has been synthesized. It was prepared by solid-state reaction of SrO:TmO 1.5 (1:2) at 9508C. It belongs to an orthorhombic system with space group Pnma. 3.2. Crystal structure of SrTm2 O4 The compound exhibits a light grey color. The X-ray powder diffraction data (see Table 1) were indexed by TREOR90 [24], the de Wolff figure of merit M20 is 80. It belongs to an orthorhombic lattice, with cell parameters ˚ b53.3781 A, ˚ c511.8193 A. ˚ According to a510.005 A, the systematic extinction, (0kl) k 1 l 5 2n 1 1 and (hl0)

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C.Q. Han et al. / Journal of Alloys and Compounds 309 (2000) 95 – 99

Fig. 3. Crystal structure of SrTm 2 O 4 . (a) Section at y50.25; (b) section at y50.75; (c) TmO 6 octahedra are shown.

C.Q. Han et al. / Journal of Alloys and Compounds 309 (2000) 95 – 99 Table 2 The structural parameters for SrTm 2 O 4

References

Atom

Position

x

y

z

˚ 2) B (A

Sr Tm1 Tm2 O1 O2 O3 O4

4c 4c 4c 4c 4c 4c 4c

0.7522(1) 0.4224(1) 0.4240(1) 0.2120(7) 0.1245(6) 0.5165(8) 0.4272(9)

0.25 0.25 0.25 0.25 0.25 0.25 0.25

0.6509(1) 0.1099(1) 0.6119(1) 0.1707(6) 0.4847(6) 0.7861(6) 0.4228(5)

0.72(8) 0.61(8) 0.51(8) 0.1(2) 0.6(2) 0.2(2) 1.1(2)

Table 3 ˚ between cations and oxygens Bond lengths (A) Tm1–O332 O1 O232 O2

2.178 2.225 2.295 2.312

Tm2–O4 O3 O432 O132

99

2.235 2.258 2.290 2.779

Sr–O432 O232 O132 O3 O3

2.615 2.636 2.726 2.748 2.850

h 5 2n 1 1, the possible space groups are Pnma or Pn2 a. Since the space group of SrYb 2 O 4 is Pnam [25], the space group of SrTm 2 O 4 probably is also Pnma. The Rietveld analysis was performed by using DBW9411 [26]. The initial model was based on the structure of SrYb 2 O 4 [24]. Good agreement between the experimental and the calculated profile with R wp 54.82% was reached. Refinement in space group Pn2 a resulted in a significantly larger R wp . This suggests that SrTm 2 O 4 is isostructural to SrYb 2 O 4 . The final result is listed in Table 2 (R p 53.39%, R wp 5 4.82%, R exp 52.21%). Fig. 2 shows the Rietveld refinement patterns. Table 3 gives the bond lengths between cations and oxygen. The crystal structure of SrTm 2 O 4 is shown in Fig. 3. From Fig. 3, each rare earth Tm 31 is bonded to six oxygens to form an octahedron. The octahedron is distorted due to the different Tm–O bond lengths. Tm1 is ˚ three coordinated by six oxygens, namely O1 at 2.225 A, ˚ ˚ ˚ O2 at 2.312 A32 and 2.295 A, two O3 at 2.178 A32. Like Tm1, Tm2 is also coordinated by two O1 at 2.779 ˚ ˚ and three O4 at 2.235 A ˚ and 2.290 A32, O3 at 2.258 A ˚A32. The Sr–O coordination is different from that of Tm–O. Each Sr has eight nearest oxygens, namely two O1 ˚ ˚ ˚ at 2.726 A32, two O2 at 2.636 A32, two O3 at 2.850 A ˚ ˚ and 2.748 A and two O4 at 2.615 A32.

Acknowledgements This work was supported by the Chinese Academy of Sciences.

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