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Preparation and investigation of the quaternary alloy CuTaInSe3
Materials Research Bulletin 42 (2007) 2067–2071 www.elsevier.com/locate/matresbu
Preparation and investigation of the quaternary alloy CuTaInSe3 P. Grima-Gallardo a,*, M. Mun˜oz a, S. Dura´n a, G.E. Delgado b, M. Quintero a, J. Ruiz a a
b
Centro de Estudios en Semiconductores (CES), Dpto. Fı´sica, Facultad de Ciencias, La Hechicera, Me´rida, Venezuela Laboratorio de Cristalografı´a, Dpto. Quı´mica, Facultad de Ciencias, Universidad de Los Andes, Me´rida 5101, Venezuela Received 29 November 2006; received in revised form 23 January 2007; accepted 1 February 2007 Available online 8 February 2007
Abstract Polycrystalline samples of the quaternary alloy CuTaInSe3 were prepared by the usual melt and anneal technique. The analysis of the diffraction pattern indicates a single phase which indexes as a tetragonal chalcopyrite-like structure with lattice parameters ˚ ; c = 11.6208 0.0007 A ˚ and V = 389 1 A ˚ 3. Differential thermal analysis shows that the melting a = 5.7837 0.0002 A transition of CuTaInSe3 is incongruent with large liquid + solids regions. # 2007 Elsevier Ltd. All rights reserved. Keywords: A. Alloys; A. Inorganic compounds; B. Chemical synthesis; C. X-ray diffraction; D. Crystal structure; D. Thermodynamic properties
1. Introduction Tantalum chalcogenides with low dimensional structures frequently display interesting physical properties such as superconductivity, charge density waves and metal-insulator transition. Therefore, their properties and structural chemistry have attracted considerable interest [1]. The study of chalcopyrite-based diluted magnetic semiconductors (ChDMSs) was a part of earlier investigation of binary II–VI and III–V diluted magnetic semiconductors (DMSs) [2–5]. Recent works on ChDMSs reported room temperature ferromagnetism and high solubility of the metal atom indicating a promissory research field [6–16]. In the past, we have reported the preparation and characterization of some ChDMSs alloys: (Cu–III–Se2)1 x(FeSe)x (III: Al, Ga and In) [17,18], (CuInSe2)1 x(CoSe)x [19], (I–InSe2)1 x(VSe)x (I: Cu and Ag) [20,21], which represent part of a systematic investigation on (AIBIIIXVI2)1 x(MT–XVI)x alloy systems where MT is a metal transition atom. In this work, the quaternary alloy CuTaInSe3 which belongs to the alloys family (CuInSe2)1 x(TaSe)x with x = 0.5 (or x = 1/3 in the alternative nomenclature (CuInSe2)1 x2(TaSe) x) was prepared and investigated. 2. Experimental procedure 2.1. Preparation of the samples Starting materials with a nominal purity of (at least) 99.99 wt.% were mixed together in the stoichiometric ratio in an evacuated and sealed quartz tube with the inner walls previously carbonized in order to prevent chemical reaction of * Corresponding author. Tel.: +58 2742401332; fax: +58 2742401286. E-mail address: [email protected] (P. Grima-Gallardo). 0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2007.02.003
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the elements with the quartz. Polycrystalline ingots of about 1 g were prepared by the melt and anneal technique: the ampoule was heated slowly to 450 8C and held there for 48 h; then the temperature was raised slowly to 1150 8C and maintained there for 24 h. Mechanical shaking of the ampoule was used during the entire heating process. After that, the ampoule was cooled to room temperature at a very low rate for 1 week. Then, the ampoule was introduced again into a furnace kept at 650 8C for one moth. Finally, the furnace was switched off and the ampoule cooled at room temperature. 2.2. Measurements 2.2.1. X-ray powder diffraction X-ray powder diffraction data were collected by means of a diffractometer (Bruker D5005) equipped with a ˚ ) at 40 kV and 20 mA. Silicon powder was used as an external graphite monochromator (Cu Ka, l = 1.54059 A standard. The samples were scanned from 5–1008 2u, with a step size of 0.028 and counting time of 20 s. The Bruker analytical software was used to establish the positions of the peaks from the a1 component and to strip mathematically the a2 components from each reflection. The peak positions were extracted by means of single-peak profile fitting carried out through the Bruker DIFFRACplus software. Each reflection was modeled by means of a pseudo-Voigt function. 2.2.2. Differential thermal analysis The differential thermal analysis (DTA) was carried out in a fully automatic Perkin-Elmer apparatus with Pt/Pt–Rh thermocouples. Au was used as an internal standard. The heating and cooling rates were controlled to 20 K/h. Transition temperatures were manually obtained from the DT versus T graph with the criteria that the transition occurs at the intersection of the base line with the slope of the thermal transition peak. The maximum error in the determination of transition temperatures by this method was estimated as 10 K. The measurements were carried out until 1450 K which is the operational limit of our DTA system.
Fig. 1. X-ray powder diffraction pattern of the alloy CuTaInSe3. The h k l-Miller indices used for indexation are showed. Some additional peaks were denoted by asterisks.
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3. Results 3.1. X-ray diffraction measurements In Fig. 1, the diffraction pattern of nominally CuTaInSe3 is presented. It has divided in two parts in order to see the high-angle region more clearly. The auto indexation was performed using the DIVOL04 software package [22] and the results are presented in Table 1. 3.2. DTA measurements In Figs. 2 and 3, the DTA heating and cooling cycles, respectively, of the alloy CuTaInSe3 are presented, together with the ternary CuInSe2 for comparison. The labels correspond to the thermal transitions according to the established criteria.
Table 1 X-ray powder diffraction data of of the alloy CuTaInSe3 2Qobs (8)
˚) dobs (A
(I/I0)obs
h
k
l
˚) dcal (A
17.142 26.668 27.730 30.923 31.808 35.561 41.891 41.999 44.188 44.297 47.825 52.248 52.446 52.966 57.772 58.043 62.666 64.077 64.421 66.453 66.951 67.197 70.820 70.988 71.452 79.813 81.194 81.415 83.712 84.046 87.138 87.450 87.600 96.174 97.490 97.804
5.16858 3.34002 3.21447 2.88944 2.81104 2.52250 2.15480 2.14951 2.04797 2.04319 1.90037 1.74943 1.74329 1.72739 1.59460 1.58779 1.48131 1.45205 1.44513 1.40578 1.39653 1.39201 1.32942 1.32669 1.31921 1.20071 1.18374 1.18108 1.15442 1.15068 1.11763 1.11444 1.11292 1.03513 1.02463 1.02218
3.5 100.0 4.0 0.4 0.4 4.4 0.9 1.2 36.3 17.6 1.0 8.2 16.7 1.1 0.1 0.2 1.0 1.1 3.5 0.2 0.4 0.3 5.5 2.4 0.9 0.3 2.8 5.0 0.1 0.5 0.8 1.0 1.5 0.2 1.1 0.6
1 1 1 2 1 2 1 2 2 2 3 1 3 2 1 3 3 0 4 2 2 4 3 3 3 4 2 4 2 4 1 3 5 4 4 4
0 1 0 0 1 1 0 1 0 2 0 1 1 1 0 2 2 0 0 2 1 1 1 3 2 1 2 2 1 3 1 3 1 3 0 4
1 2 3 0 3 1 5 3 4 0 1 6 2 5 7 1 3 8 0 6 7 1 6 2 5 5 8 4 9 1 10 6 2 5 8 0
5.16746 3.34007 3.21451 2.88869 2.80936 2.52238 2.15485 2.14938 2.04802 2.04333 1.90061 1.74935 1.74351 1.72773 1.59481 1.58818 1.48132 1.45190 1.44523 1.40552 1.39647 1.39201 1.32920 1.32663 1.31964 1.20053 1.18380 1.18108 1.15487 1.15067 1.11747 1.11443 1.11291 1.03529 1.02450 1.02215
˚ ; c = 11.6208 0.0007 A ˚ ; V = 389 1 A ˚ 3. Tetragonal system: a = 5.7837 0.0002 A
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Fig. 2. DTA heating cycle for the alloy CuTaInSe3 and the ternary CuInSe2.
Fig. 3. DTA cooling cycle for the alloy CuTaInSe3 and the ternary CuInSe2.
4. Discussion The diffraction pattern of nominally CuTaInSe3 shows only one phase. The sharpness of the diffraction peaks denotes a good crystallization of the sample and good thermal equilibrium. Some little peaks denoted by asterisks cannot be indexed; we think that could be some impurities or oxides. The observed phase indexes as a tetragonal chalcopyrite-like structure with unit cell parameters ˚ ; c = 11.6208 0.0007 A ˚ and V = 389 1 A ˚ 3, which are very close to the CuInSe2 parent a = 5.7837 0.0002 A 3 ˚ ˚ ˚ structure (a = 5.780 A; c = 11.56 A and V = 386 A ) indicating the high solubility of the Ta-atom in CuInSe2. The DTA analysis shows that the area under the peaks for CuInSe2 are much bigger than for CuTaInSe3, i.e. CuTaInSe3 is less stable that CuInSe2; similar behavior has been observed in other quaternary compounds previously studied (CuFeInSe3, CuFeAlSe3, CuFeGaSe3, CuCoInSe3, CuVInSe3 and AgVInSe3; see references given in Section 1). In the heating cycle for CuInSe2, there are only two thermal transitions, the order-disorder and the melting, but for CuTaInSe3
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almost four thermal transitions are clearly observed. Analogous behavior occurs in the cooling cycle. This is indicative of an incongruent melting with large liquid + solids regions. Experiments with compositions in the interval 0 < x < 0.5 are in course in order to obtain the corresponding phase diagram and will be published in the near future. 5. Conclusions CuTaInSe3 is an ordered single-phase alloy with unit cell parameters very close to the parent ternary CuInSe2 indicating a high solubility of the Ta-atom in the chalcopyrite structure. The thermal analysis shows several transformations suggesting a complicated phase diagram for the entire alloy family (CuInSe2)1 x(TaSe)x. Acknowledgments The authors want to thanks to CDCHT project number C-1440-06-05-B for financial support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
J.H. Zhang, F. Chen, J. Li, Ch.J. O’Connor, J. Appl. Phys. 81 (1997) 5283. A. Twardowski, C.J.M. Denissen, W.J.M. de Jonge, A.T.A.M. de Waele, M. Demianiuk, R. Triboulet, Solid State Commun. 59 (1986) 199. A. Twardowski, H.J.M. Swagten, W.J.M. de Jonge, M. Demianiuk, Phys. Rev. B36 (1987) 7013. P.M. Shand, A. Lewicki, I. Miotkowski, B.C. Crooker, J.K. Furdyna, Phys. Rev. B44 (1991) 6152. A. Lewicki, A.I. Schindler, P.M. Shand, B.C. Crooker, J.K. Furdyna, Phys. Rev. B44 (1991) 6137. G.A. Medvedkin, T. Ishibashi, T. Nishi, K. Hayata, Y. Hasegawa, K. Sato, Jpn. J. Appl. Phys. 39 (2000) L949. K. Sato, G.A. Medvedkin, T. Ishibashi, J. Cryst. Growth 236 (2002) 609. R. Tovar, M. Quintero, Ch. Neal, J.C. Woolley, J. Cryst. Growth 106 (1990) 629. M. Quintero, P. Grima-Gallardo, R. Tovar, G.S. Pe´rez, J.C. Woolley, Phys. Status Solidi (A) 107 (1988) 205. G. Lamarche, J.C. Woolley, R. Tovar, M. Quintero, V. Sagredo, J. Magn. Magn. Mater. 80 (1989) 321. R. Tovar, Ph.D. Thesis, Universite´ des Sciences et Technologies de Lille, France, 1995, unpublished. M. Quintero, R. Tovar, M. Dhesi, J.C. Woolley, Phys. Status Solidi (A) 115 (1989) 157. Ch. Neal, J.C. Woolley, R. Tovar, M. Quintero, J. Phys. D: Appl. Phys. 22 (1989) 1347. R. Tovar, M. Quintero, C. Neal, J.C. Woolley, J. Electrochem. Soc. 137 (1990) 2327. M. Quintero, P. Grima-Gallardo, J.E. Avon, G. Lamarche, J.C. Woolley, Phys. Status Solidi (A) 108 (1988) 599. M. Quintero, P. Grima-Gallardo, R. Tovar, R. Goudreault, D. Bissonnette, G. Lamarche, J.C. Woolley, J. Solid State Chem. 76 (1988) 210. P. Grima-Gallardo, K. Ca´rdenas, M. Quintero, J. Ruiz, G. Delgado, Mater. Res. Bull. 36 (2001) 861. P. Grima-Gallardo, K. Ca´rdenas, L. Molina, M. Quintero, J. Ruiz, G. Delgado, Phys. Status Solidi (A) 187 (2001) 395. P. Grima-Gallardo, M. Mun˜oz, J. Ruiz, C. Power, J. Gonza´lez, Y. Legodec, P. Munsch, J.P. Itie´, V. Bricen˜o, J.M. Bricen˜o, Phys. Status Solidi (B) 241 (2004) 1795. [20] P. Grima-Gallardo, S. Dura´n, M. Quintero, M. Mun˜oz, G. Delgado, J.M. Bricen˜o, H. Romero, J. Ruiz, Phys. Status Solidi (A) 193 (2002) 217. [21] S. Dura´n, P. Grima-Gallardo, l.M. Mun˜oz, M. Quintero, J. Ruiz, L. Ceballos, J.M. Bricen˜o, H. Romero, Phys. Status Solidi (C) 2 (2005) 3766. [22] A. Boultif, D. Lo¨uer, J. Appl. Cryst. 37 (2004) 724.
Preparation and investigation of the quaternary alloy CuTaInSe3 P. Grima-Gallardo a,*, M. Mun˜oz a, S. Dura´n a, G.E. Delgado b, M. Quintero a, J. Ruiz a a
b
Centro de Estudios en Semiconductores (CES), Dpto. Fı´sica, Facultad de Ciencias, La Hechicera, Me´rida, Venezuela Laboratorio de Cristalografı´a, Dpto. Quı´mica, Facultad de Ciencias, Universidad de Los Andes, Me´rida 5101, Venezuela Received 29 November 2006; received in revised form 23 January 2007; accepted 1 February 2007 Available online 8 February 2007
Abstract Polycrystalline samples of the quaternary alloy CuTaInSe3 were prepared by the usual melt and anneal technique. The analysis of the diffraction pattern indicates a single phase which indexes as a tetragonal chalcopyrite-like structure with lattice parameters ˚ ; c = 11.6208 0.0007 A ˚ and V = 389 1 A ˚ 3. Differential thermal analysis shows that the melting a = 5.7837 0.0002 A transition of CuTaInSe3 is incongruent with large liquid + solids regions. # 2007 Elsevier Ltd. All rights reserved. Keywords: A. Alloys; A. Inorganic compounds; B. Chemical synthesis; C. X-ray diffraction; D. Crystal structure; D. Thermodynamic properties
1. Introduction Tantalum chalcogenides with low dimensional structures frequently display interesting physical properties such as superconductivity, charge density waves and metal-insulator transition. Therefore, their properties and structural chemistry have attracted considerable interest [1]. The study of chalcopyrite-based diluted magnetic semiconductors (ChDMSs) was a part of earlier investigation of binary II–VI and III–V diluted magnetic semiconductors (DMSs) [2–5]. Recent works on ChDMSs reported room temperature ferromagnetism and high solubility of the metal atom indicating a promissory research field [6–16]. In the past, we have reported the preparation and characterization of some ChDMSs alloys: (Cu–III–Se2)1 x(FeSe)x (III: Al, Ga and In) [17,18], (CuInSe2)1 x(CoSe)x [19], (I–InSe2)1 x(VSe)x (I: Cu and Ag) [20,21], which represent part of a systematic investigation on (AIBIIIXVI2)1 x(MT–XVI)x alloy systems where MT is a metal transition atom. In this work, the quaternary alloy CuTaInSe3 which belongs to the alloys family (CuInSe2)1 x(TaSe)x with x = 0.5 (or x = 1/3 in the alternative nomenclature (CuInSe2)1 x2(TaSe) x) was prepared and investigated. 2. Experimental procedure 2.1. Preparation of the samples Starting materials with a nominal purity of (at least) 99.99 wt.% were mixed together in the stoichiometric ratio in an evacuated and sealed quartz tube with the inner walls previously carbonized in order to prevent chemical reaction of * Corresponding author. Tel.: +58 2742401332; fax: +58 2742401286. E-mail address: [email protected] (P. Grima-Gallardo). 0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2007.02.003
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the elements with the quartz. Polycrystalline ingots of about 1 g were prepared by the melt and anneal technique: the ampoule was heated slowly to 450 8C and held there for 48 h; then the temperature was raised slowly to 1150 8C and maintained there for 24 h. Mechanical shaking of the ampoule was used during the entire heating process. After that, the ampoule was cooled to room temperature at a very low rate for 1 week. Then, the ampoule was introduced again into a furnace kept at 650 8C for one moth. Finally, the furnace was switched off and the ampoule cooled at room temperature. 2.2. Measurements 2.2.1. X-ray powder diffraction X-ray powder diffraction data were collected by means of a diffractometer (Bruker D5005) equipped with a ˚ ) at 40 kV and 20 mA. Silicon powder was used as an external graphite monochromator (Cu Ka, l = 1.54059 A standard. The samples were scanned from 5–1008 2u, with a step size of 0.028 and counting time of 20 s. The Bruker analytical software was used to establish the positions of the peaks from the a1 component and to strip mathematically the a2 components from each reflection. The peak positions were extracted by means of single-peak profile fitting carried out through the Bruker DIFFRACplus software. Each reflection was modeled by means of a pseudo-Voigt function. 2.2.2. Differential thermal analysis The differential thermal analysis (DTA) was carried out in a fully automatic Perkin-Elmer apparatus with Pt/Pt–Rh thermocouples. Au was used as an internal standard. The heating and cooling rates were controlled to 20 K/h. Transition temperatures were manually obtained from the DT versus T graph with the criteria that the transition occurs at the intersection of the base line with the slope of the thermal transition peak. The maximum error in the determination of transition temperatures by this method was estimated as 10 K. The measurements were carried out until 1450 K which is the operational limit of our DTA system.
Fig. 1. X-ray powder diffraction pattern of the alloy CuTaInSe3. The h k l-Miller indices used for indexation are showed. Some additional peaks were denoted by asterisks.
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3. Results 3.1. X-ray diffraction measurements In Fig. 1, the diffraction pattern of nominally CuTaInSe3 is presented. It has divided in two parts in order to see the high-angle region more clearly. The auto indexation was performed using the DIVOL04 software package [22] and the results are presented in Table 1. 3.2. DTA measurements In Figs. 2 and 3, the DTA heating and cooling cycles, respectively, of the alloy CuTaInSe3 are presented, together with the ternary CuInSe2 for comparison. The labels correspond to the thermal transitions according to the established criteria.
Table 1 X-ray powder diffraction data of of the alloy CuTaInSe3 2Qobs (8)
˚) dobs (A
(I/I0)obs
h
k
l
˚) dcal (A
17.142 26.668 27.730 30.923 31.808 35.561 41.891 41.999 44.188 44.297 47.825 52.248 52.446 52.966 57.772 58.043 62.666 64.077 64.421 66.453 66.951 67.197 70.820 70.988 71.452 79.813 81.194 81.415 83.712 84.046 87.138 87.450 87.600 96.174 97.490 97.804
5.16858 3.34002 3.21447 2.88944 2.81104 2.52250 2.15480 2.14951 2.04797 2.04319 1.90037 1.74943 1.74329 1.72739 1.59460 1.58779 1.48131 1.45205 1.44513 1.40578 1.39653 1.39201 1.32942 1.32669 1.31921 1.20071 1.18374 1.18108 1.15442 1.15068 1.11763 1.11444 1.11292 1.03513 1.02463 1.02218
3.5 100.0 4.0 0.4 0.4 4.4 0.9 1.2 36.3 17.6 1.0 8.2 16.7 1.1 0.1 0.2 1.0 1.1 3.5 0.2 0.4 0.3 5.5 2.4 0.9 0.3 2.8 5.0 0.1 0.5 0.8 1.0 1.5 0.2 1.1 0.6
1 1 1 2 1 2 1 2 2 2 3 1 3 2 1 3 3 0 4 2 2 4 3 3 3 4 2 4 2 4 1 3 5 4 4 4
0 1 0 0 1 1 0 1 0 2 0 1 1 1 0 2 2 0 0 2 1 1 1 3 2 1 2 2 1 3 1 3 1 3 0 4
1 2 3 0 3 1 5 3 4 0 1 6 2 5 7 1 3 8 0 6 7 1 6 2 5 5 8 4 9 1 10 6 2 5 8 0
5.16746 3.34007 3.21451 2.88869 2.80936 2.52238 2.15485 2.14938 2.04802 2.04333 1.90061 1.74935 1.74351 1.72773 1.59481 1.58818 1.48132 1.45190 1.44523 1.40552 1.39647 1.39201 1.32920 1.32663 1.31964 1.20053 1.18380 1.18108 1.15487 1.15067 1.11747 1.11443 1.11291 1.03529 1.02450 1.02215
˚ ; c = 11.6208 0.0007 A ˚ ; V = 389 1 A ˚ 3. Tetragonal system: a = 5.7837 0.0002 A
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Fig. 2. DTA heating cycle for the alloy CuTaInSe3 and the ternary CuInSe2.
Fig. 3. DTA cooling cycle for the alloy CuTaInSe3 and the ternary CuInSe2.
4. Discussion The diffraction pattern of nominally CuTaInSe3 shows only one phase. The sharpness of the diffraction peaks denotes a good crystallization of the sample and good thermal equilibrium. Some little peaks denoted by asterisks cannot be indexed; we think that could be some impurities or oxides. The observed phase indexes as a tetragonal chalcopyrite-like structure with unit cell parameters ˚ ; c = 11.6208 0.0007 A ˚ and V = 389 1 A ˚ 3, which are very close to the CuInSe2 parent a = 5.7837 0.0002 A 3 ˚ ˚ ˚ structure (a = 5.780 A; c = 11.56 A and V = 386 A ) indicating the high solubility of the Ta-atom in CuInSe2. The DTA analysis shows that the area under the peaks for CuInSe2 are much bigger than for CuTaInSe3, i.e. CuTaInSe3 is less stable that CuInSe2; similar behavior has been observed in other quaternary compounds previously studied (CuFeInSe3, CuFeAlSe3, CuFeGaSe3, CuCoInSe3, CuVInSe3 and AgVInSe3; see references given in Section 1). In the heating cycle for CuInSe2, there are only two thermal transitions, the order-disorder and the melting, but for CuTaInSe3
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almost four thermal transitions are clearly observed. Analogous behavior occurs in the cooling cycle. This is indicative of an incongruent melting with large liquid + solids regions. Experiments with compositions in the interval 0 < x < 0.5 are in course in order to obtain the corresponding phase diagram and will be published in the near future. 5. Conclusions CuTaInSe3 is an ordered single-phase alloy with unit cell parameters very close to the parent ternary CuInSe2 indicating a high solubility of the Ta-atom in the chalcopyrite structure. The thermal analysis shows several transformations suggesting a complicated phase diagram for the entire alloy family (CuInSe2)1 x(TaSe)x. Acknowledgments The authors want to thanks to CDCHT project number C-1440-06-05-B for financial support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
J.H. Zhang, F. Chen, J. Li, Ch.J. O’Connor, J. Appl. Phys. 81 (1997) 5283. A. Twardowski, C.J.M. Denissen, W.J.M. de Jonge, A.T.A.M. de Waele, M. Demianiuk, R. Triboulet, Solid State Commun. 59 (1986) 199. A. Twardowski, H.J.M. Swagten, W.J.M. de Jonge, M. Demianiuk, Phys. Rev. B36 (1987) 7013. P.M. Shand, A. Lewicki, I. Miotkowski, B.C. Crooker, J.K. Furdyna, Phys. Rev. B44 (1991) 6152. A. Lewicki, A.I. Schindler, P.M. Shand, B.C. Crooker, J.K. Furdyna, Phys. Rev. B44 (1991) 6137. G.A. Medvedkin, T. Ishibashi, T. Nishi, K. Hayata, Y. Hasegawa, K. Sato, Jpn. J. Appl. Phys. 39 (2000) L949. K. Sato, G.A. Medvedkin, T. Ishibashi, J. Cryst. Growth 236 (2002) 609. R. Tovar, M. Quintero, Ch. Neal, J.C. Woolley, J. Cryst. Growth 106 (1990) 629. M. Quintero, P. Grima-Gallardo, R. Tovar, G.S. Pe´rez, J.C. Woolley, Phys. Status Solidi (A) 107 (1988) 205. G. Lamarche, J.C. Woolley, R. Tovar, M. Quintero, V. Sagredo, J. Magn. Magn. Mater. 80 (1989) 321. R. Tovar, Ph.D. Thesis, Universite´ des Sciences et Technologies de Lille, France, 1995, unpublished. M. Quintero, R. Tovar, M. Dhesi, J.C. Woolley, Phys. Status Solidi (A) 115 (1989) 157. Ch. Neal, J.C. Woolley, R. Tovar, M. Quintero, J. Phys. D: Appl. Phys. 22 (1989) 1347. R. Tovar, M. Quintero, C. Neal, J.C. Woolley, J. Electrochem. Soc. 137 (1990) 2327. M. Quintero, P. Grima-Gallardo, J.E. Avon, G. Lamarche, J.C. Woolley, Phys. Status Solidi (A) 108 (1988) 599. M. Quintero, P. Grima-Gallardo, R. Tovar, R. Goudreault, D. Bissonnette, G. Lamarche, J.C. Woolley, J. Solid State Chem. 76 (1988) 210. P. Grima-Gallardo, K. Ca´rdenas, M. Quintero, J. Ruiz, G. Delgado, Mater. Res. Bull. 36 (2001) 861. P. Grima-Gallardo, K. Ca´rdenas, L. Molina, M. Quintero, J. Ruiz, G. Delgado, Phys. Status Solidi (A) 187 (2001) 395. P. Grima-Gallardo, M. Mun˜oz, J. Ruiz, C. Power, J. Gonza´lez, Y. Legodec, P. Munsch, J.P. Itie´, V. Bricen˜o, J.M. Bricen˜o, Phys. Status Solidi (B) 241 (2004) 1795. [20] P. Grima-Gallardo, S. Dura´n, M. Quintero, M. Mun˜oz, G. Delgado, J.M. Bricen˜o, H. Romero, J. Ruiz, Phys. Status Solidi (A) 193 (2002) 217. [21] S. Dura´n, P. Grima-Gallardo, l.M. Mun˜oz, M. Quintero, J. Ruiz, L. Ceballos, J.M. Bricen˜o, H. Romero, Phys. Status Solidi (C) 2 (2005) 3766. [22] A. Boultif, D. Lo¨uer, J. Appl. Cryst. 37 (2004) 724.