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Composition and structure of two hitherto unidentified phases in the system La2O3-NiO-O
Journal of the Less-Common
215
Metals, 79 (1981) 215 - 219
COMPOSITION AND STRUCTURE OF TWO HITHERTO UNIDENTIFIED PHASES IN THE SYSTEM La203-NiO-0
CESARE BRISI, MARIO VALLINO and FEDELE ABBATTISTA Istituto Waly)
di Chimica Generale e Applicata
e di Metallurgia
de1 Politecnico
di Torino,
Turin
(Received July 12, 1980; in revised form October 19, 1980)
Summary
The compound LadNisO1,, can be obtained in a mechanical mixture with NiO by heating LaNiOs at, 1100 “C in air. It has an orthorhombic structure of the SrqTi30r0 modified type. By heating La(NOs)s and Ni(NOs)s in a molecular ratio of 4/3 at 1100 “C!at first a mixture of NiO and a compound with the formula LasNiz07 is obtained which slowly changes to I.a~NisOlO. The compound LasNisO, also belongs to the orthorhombic system with a structure of the SrsTisO, modified type.
1. Introduction
The existence of the compounds LaNiOs, with a deformed perovskite structure [ 1], and LasNi04, with a structure of the KsNiF4 type [2] , in the system LaPOs-NiO-0 is well known. Another phase having the composition LaNi20s.s6, with a structure similar to that of CaFesO,, has recently been prepared by Sieler and Kaiser [ 31. Some workers have reported the existence of yet another phase, the composition and structure of which are unknown although the ratio La/Ni probably lies between that of LaNiOs and that of LazNiOl. This phase was first observed by Wold and Amott [4], who obtained it in a mechanical mixture with NiO by heating LaNiOs to 1100 “C. For this phase they report only a few reflections, obviously not indexed, derived from the X-ray pattern. Arjomand and Machin [5] have obtained an analogous X-ray spectrogram by heating mixtures of La(NOs)s and Ni(NOs)s between 500 and 800 “C; the relative proportions are not given. The phase reported by these workers [4,5] is probably to be identified with that, also of unknown composition, obtained by Nakamura et al. [6] as an intermediate reduction product of LaNiOs at 1000 “C. The composition and structure of this hitherto unidentified phase, and of yet another phase that does not appear to have been mentioned in the literature, are considered in this work. 0022-5088/81/0000-0000/$02.50
@ Elsevier Sequoia/Printed
in The Netherlands
216
2. Experimental details and results Following the procedure laid down by Wold and Arnott [ 43 we first prepared LaNiOs by heating the powder obtained by dry drawing an equimolecular solution of La(N03)a and Ni(NOa)s in air at 800 “C for approximately 100 h. Iodometric analysis showed that the composition of LaNiOs prepared in this way is virtually stoichiometric: the observed weight percentage of active oxygen, i.e. the oxygen in excess of that corresponding to nickel with an oxidation number of two, is 3.1 + 0.2 wt.% compared with a calculated value of 3.26 wt.%. The compound so prepared was then heated at 1100 “C in air for approximately 30 min; X-ray analysis showed that the solid obtained in this way was composed of a mechanical mixture of NiO and a second phase, the characteristic reflections of which could ah be arranged (see Table 1) as required for an elementary orthorhombic cell having the lattice parameters a0 = 5.417 * 0.004 8, b0 = 5.480 ? 0.004 A and co = 27.96 f 0.02 A. The size of the cell, the extinctions observed and the relative line intensities clearly show that the structure of this phase is analogous to that of the compound La4C03010 recently reported by Sepplinen and Tikkanen [7] and by Janacek and Wirtz [8] and to that of a series of phases of general formula La4MezMgOIo prepared recently by us [9] . This structure is similar to that of SrqTi3010 which is derived by the insertion of SrO layers between triple perovskite blocks [IO]. The formula for the new phase is therefore La4NisO10; this is further confirmed by the weight loss which results from heating LaNiOa to 1100 “C, namely (1.65 f. 0.05)% which is very close to the theoretical value (1.63%) calculated according to the reaction 4LaNi03 -+ La4Ni3010 + NiO + i O2 As the composition of LaNiOs is very close to the stoichiometric composition, then that of the new phase is very close to the composition theoretically corresponding to the formula LadNiaOIO; this means that the percentage of vacant positions in the lattice of oxygen ions (a phenomenon which often occurs in compounds of this type) is negligible in the product obtained in air at 1100 “C, Sr4Ti3010 has a tetragonal elementary cell, the base of which is equal to that of the simple SrTiOa perovskite cell; in contrast, the phase LarNiaOlo, as well as the analogous compound containing cobalt and the compounds of the LalMezMgOlo series, presents a slightly deformed lattice and its elementary cell becomes orthorhombic with a0 and b. values close to the diagonal of the base of the ideal tetragonal cell. The atoms or group of atoms that in the simple tetragonal cell form bodycentred sublattices in the new cell form instead facecentred sublattices. La4Ni3010 appears to be thermodynamically stable, since it showed no signs of decomposition when held at 1100 “c for very long periods. This suggested that it could be prepared by direct synthesis. We there-
217 TABLE 1 X-ray powder pattern of LadNig010 hkl
d ObS
d talc
I
111 113 008 115 0.0.10 117 020 200 119 028 208 1.1.11 0.0.14 0.2.10 220 1.1.13 0.0.16 131 311 228 1.1.15 0.2.14 2.0.14 137 2.2.10 317 0.0.18 1.1.17
3.814 3.558 3.495 3.170 2.796 2.774 2.740 2.708 2.417 2.157 2.141 2.122 1.998 1.957 1.926 1.877 1.749 1.727 1.712 1.687 1.678 1.616 1.610
3.816 3.560 3.495 3.172 2.796 2.773 2.740 2.708 2.418 2.156 2.141 2.122 1.997 1.957 1.926 1.878 1.747 1.728 1.712 1.687 1.678 1.614 1.607 1.588 1.586 1.576 1.553 1.513
18 5 15 3 15 100 40 40 8 12 10 8 14 2 35 2 5 3 2 8 10 5 5
1.588 1.578 1.553 1.514
16 10 2 3
Philips X-ray diffractometer with silicon as an internal standard (00 = 5.4306 A). Orthorhomhic: a0 = 5.417 j: 0.004 A, bo = 5.480 * 0.004 A, co = 27.96 f. 0.02 A.
fore attempted this by heating to 1100 “C!the residue obtained from the evaporation of solutions of La(NOs)a and Ni(NOs)a with an atomic ratio La/Ni of 4/3. The X-ray spectrograms of the solids obtained after relatively short (about 24 h) periods of heating, however, did not display the lines of LalNiBOIO; a series of reflections was found (Table 2) which could be arranged as required for an elementary orthorhombic cell having the lattice parameters a0 = 5.407 r 0.004 A, b. = 5.454 + 0.004 A and co = 20.54 + 0.02 A, and close to which the lines characteristic of NiO were very weakly observable. The size of the cell, the extinctions and the relative intensities correspond fully to a structure similar to that of Sr3Ti207, which is derived by the insertion of an SrO layer between two perovskite SrTiO, blocks 171.
218 TABLE 2 X-ray powder pattern of La3Ni207 hkl
d ob
dd
Z
111 006 113 115 020 200 117 026 206 0.0.10 119 220 131 0.0.12 311 1.1.11 226 I 133 0.2.10 2.0.10 135 315
3.773 3.422 3.347 2.807 2.727 2.703 2.275 2.132 2.122 2.055 1.961 1.920 1.717 1.712 1.707
3.774 3.423 3.349 2.805 2.727 2.703 2.275 2.133 2.122 2.054 1.962 1.920 1.717 1.712 1.705 1.679 1.675 1.671 1.641 1.636 1.589 1.580
18 10 5 100 42 40 5 12 14 6 2 40 3 3 3
1.674 1.641 1.636 1.590 1.579
15 4 5 18 16
Philips X-ray diffractometer with silicon as an internal standard (~0 = 5.4306 A). Orthorhombic: ao = 5.407 * 0.004 A, bo = 5.454 * 0.004 A, co = 20.54 f 0.02 A.
However, once again there is a slight deformation with a transition from the tetragonal to an orthorhombic cell. We must therefore draw the conclusion that the solid obtained under the conditions described here consists of a mixture of NiO and a hitherto unreported compound corresponding to the formula La3Ni207 and having the type of structure just described. After protracted heating the lines of the new compound gradually weaken and give way to increasingly intense La,Ni3010 reflections. At the same time the NiO lines weaken to the point of virtual disappearance. However, the reaction 4La3Ni207 + NiO +i02
+ 3LalNi3010
appears to be very slow, since even after 800 h at 1100 “C small amounts of La3Ni207 could still be detected. Similar phenomena, i.e. the initial formation of La3Ni207 and its gradual conversion to LabNi3Or0 , can also be observed by heating to 1100 “C mixtures of La(N03)3 and Ni(N03)2 with a ratio La/Ni of 3/2. This suggests that La3Ni207 is, at least at 1100 “C, a metastable phase.
219
References 1 2 3 4 5 6 7 8 9
A. Wold, B. Post and E. Banks, J. Am. Chem. Sot., 79 (1957) 4911. A. Rabenau and P. Eckerlin, Acta Crystallogr., 11 (1958) 304. J. Sieler and J. Kaiser, Z. Anorg. Allg. Chem., 377 (1970) 316. A. Wold and R. J. Amott, J. Phys. Chem. Solids, 9 (1959) 176. M. Arjomand and D. J. Machin, J. Chem. Sot., Dalton Trans., (1975) 1055. T. Nakamura, G. Petzow and L. J. Gauckel, Mater. Res. Bull., 14 (1979) 649. M. Seppiinen and M. G. Tikkanen, Acta Chem. Stand.. Ser. A, 30 (1979) 389. J. J. Janacek and G. P. Wirtz, J. Am. Ceram. Sot., 61 (1978) 342. F. Abbattista, M. Vallino and C. Brisi, Atti Accad. Sci. Torino, Cl. Sci. Fis., Nat. Mat., 114 (1980). 10 S. N. Ruddlesden and P. Popper, Acta Crystallogr., 11 (1958) 54.
215
Metals, 79 (1981) 215 - 219
COMPOSITION AND STRUCTURE OF TWO HITHERTO UNIDENTIFIED PHASES IN THE SYSTEM La203-NiO-0
CESARE BRISI, MARIO VALLINO and FEDELE ABBATTISTA Istituto Waly)
di Chimica Generale e Applicata
e di Metallurgia
de1 Politecnico
di Torino,
Turin
(Received July 12, 1980; in revised form October 19, 1980)
Summary
The compound LadNisO1,, can be obtained in a mechanical mixture with NiO by heating LaNiOs at, 1100 “C in air. It has an orthorhombic structure of the SrqTi30r0 modified type. By heating La(NOs)s and Ni(NOs)s in a molecular ratio of 4/3 at 1100 “C!at first a mixture of NiO and a compound with the formula LasNiz07 is obtained which slowly changes to I.a~NisOlO. The compound LasNisO, also belongs to the orthorhombic system with a structure of the SrsTisO, modified type.
1. Introduction
The existence of the compounds LaNiOs, with a deformed perovskite structure [ 1], and LasNi04, with a structure of the KsNiF4 type [2] , in the system LaPOs-NiO-0 is well known. Another phase having the composition LaNi20s.s6, with a structure similar to that of CaFesO,, has recently been prepared by Sieler and Kaiser [ 31. Some workers have reported the existence of yet another phase, the composition and structure of which are unknown although the ratio La/Ni probably lies between that of LaNiOs and that of LazNiOl. This phase was first observed by Wold and Amott [4], who obtained it in a mechanical mixture with NiO by heating LaNiOs to 1100 “C. For this phase they report only a few reflections, obviously not indexed, derived from the X-ray pattern. Arjomand and Machin [5] have obtained an analogous X-ray spectrogram by heating mixtures of La(NOs)s and Ni(NOs)s between 500 and 800 “C; the relative proportions are not given. The phase reported by these workers [4,5] is probably to be identified with that, also of unknown composition, obtained by Nakamura et al. [6] as an intermediate reduction product of LaNiOs at 1000 “C. The composition and structure of this hitherto unidentified phase, and of yet another phase that does not appear to have been mentioned in the literature, are considered in this work. 0022-5088/81/0000-0000/$02.50
@ Elsevier Sequoia/Printed
in The Netherlands
216
2. Experimental details and results Following the procedure laid down by Wold and Arnott [ 43 we first prepared LaNiOs by heating the powder obtained by dry drawing an equimolecular solution of La(N03)a and Ni(NOa)s in air at 800 “C for approximately 100 h. Iodometric analysis showed that the composition of LaNiOs prepared in this way is virtually stoichiometric: the observed weight percentage of active oxygen, i.e. the oxygen in excess of that corresponding to nickel with an oxidation number of two, is 3.1 + 0.2 wt.% compared with a calculated value of 3.26 wt.%. The compound so prepared was then heated at 1100 “C in air for approximately 30 min; X-ray analysis showed that the solid obtained in this way was composed of a mechanical mixture of NiO and a second phase, the characteristic reflections of which could ah be arranged (see Table 1) as required for an elementary orthorhombic cell having the lattice parameters a0 = 5.417 * 0.004 8, b0 = 5.480 ? 0.004 A and co = 27.96 f 0.02 A. The size of the cell, the extinctions observed and the relative line intensities clearly show that the structure of this phase is analogous to that of the compound La4C03010 recently reported by Sepplinen and Tikkanen [7] and by Janacek and Wirtz [8] and to that of a series of phases of general formula La4MezMgOIo prepared recently by us [9] . This structure is similar to that of SrqTi3010 which is derived by the insertion of SrO layers between triple perovskite blocks [IO]. The formula for the new phase is therefore La4NisO10; this is further confirmed by the weight loss which results from heating LaNiOa to 1100 “C, namely (1.65 f. 0.05)% which is very close to the theoretical value (1.63%) calculated according to the reaction 4LaNi03 -+ La4Ni3010 + NiO + i O2 As the composition of LaNiOs is very close to the stoichiometric composition, then that of the new phase is very close to the composition theoretically corresponding to the formula LadNiaOIO; this means that the percentage of vacant positions in the lattice of oxygen ions (a phenomenon which often occurs in compounds of this type) is negligible in the product obtained in air at 1100 “C, Sr4Ti3010 has a tetragonal elementary cell, the base of which is equal to that of the simple SrTiOa perovskite cell; in contrast, the phase LarNiaOlo, as well as the analogous compound containing cobalt and the compounds of the LalMezMgOlo series, presents a slightly deformed lattice and its elementary cell becomes orthorhombic with a0 and b. values close to the diagonal of the base of the ideal tetragonal cell. The atoms or group of atoms that in the simple tetragonal cell form bodycentred sublattices in the new cell form instead facecentred sublattices. La4Ni3010 appears to be thermodynamically stable, since it showed no signs of decomposition when held at 1100 “c for very long periods. This suggested that it could be prepared by direct synthesis. We there-
217 TABLE 1 X-ray powder pattern of LadNig010 hkl
d ObS
d talc
I
111 113 008 115 0.0.10 117 020 200 119 028 208 1.1.11 0.0.14 0.2.10 220 1.1.13 0.0.16 131 311 228 1.1.15 0.2.14 2.0.14 137 2.2.10 317 0.0.18 1.1.17
3.814 3.558 3.495 3.170 2.796 2.774 2.740 2.708 2.417 2.157 2.141 2.122 1.998 1.957 1.926 1.877 1.749 1.727 1.712 1.687 1.678 1.616 1.610
3.816 3.560 3.495 3.172 2.796 2.773 2.740 2.708 2.418 2.156 2.141 2.122 1.997 1.957 1.926 1.878 1.747 1.728 1.712 1.687 1.678 1.614 1.607 1.588 1.586 1.576 1.553 1.513
18 5 15 3 15 100 40 40 8 12 10 8 14 2 35 2 5 3 2 8 10 5 5
1.588 1.578 1.553 1.514
16 10 2 3
Philips X-ray diffractometer with silicon as an internal standard (00 = 5.4306 A). Orthorhomhic: a0 = 5.417 j: 0.004 A, bo = 5.480 * 0.004 A, co = 27.96 f. 0.02 A.
fore attempted this by heating to 1100 “C!the residue obtained from the evaporation of solutions of La(NOs)a and Ni(NOs)a with an atomic ratio La/Ni of 4/3. The X-ray spectrograms of the solids obtained after relatively short (about 24 h) periods of heating, however, did not display the lines of LalNiBOIO; a series of reflections was found (Table 2) which could be arranged as required for an elementary orthorhombic cell having the lattice parameters a0 = 5.407 r 0.004 A, b. = 5.454 + 0.004 A and co = 20.54 + 0.02 A, and close to which the lines characteristic of NiO were very weakly observable. The size of the cell, the extinctions and the relative intensities correspond fully to a structure similar to that of Sr3Ti207, which is derived by the insertion of an SrO layer between two perovskite SrTiO, blocks 171.
218 TABLE 2 X-ray powder pattern of La3Ni207 hkl
d ob
dd
Z
111 006 113 115 020 200 117 026 206 0.0.10 119 220 131 0.0.12 311 1.1.11 226 I 133 0.2.10 2.0.10 135 315
3.773 3.422 3.347 2.807 2.727 2.703 2.275 2.132 2.122 2.055 1.961 1.920 1.717 1.712 1.707
3.774 3.423 3.349 2.805 2.727 2.703 2.275 2.133 2.122 2.054 1.962 1.920 1.717 1.712 1.705 1.679 1.675 1.671 1.641 1.636 1.589 1.580
18 10 5 100 42 40 5 12 14 6 2 40 3 3 3
1.674 1.641 1.636 1.590 1.579
15 4 5 18 16
Philips X-ray diffractometer with silicon as an internal standard (~0 = 5.4306 A). Orthorhombic: ao = 5.407 * 0.004 A, bo = 5.454 * 0.004 A, co = 20.54 f 0.02 A.
However, once again there is a slight deformation with a transition from the tetragonal to an orthorhombic cell. We must therefore draw the conclusion that the solid obtained under the conditions described here consists of a mixture of NiO and a hitherto unreported compound corresponding to the formula La3Ni207 and having the type of structure just described. After protracted heating the lines of the new compound gradually weaken and give way to increasingly intense La,Ni3010 reflections. At the same time the NiO lines weaken to the point of virtual disappearance. However, the reaction 4La3Ni207 + NiO +i02
+ 3LalNi3010
appears to be very slow, since even after 800 h at 1100 “C small amounts of La3Ni207 could still be detected. Similar phenomena, i.e. the initial formation of La3Ni207 and its gradual conversion to LabNi3Or0 , can also be observed by heating to 1100 “C mixtures of La(N03)3 and Ni(N03)2 with a ratio La/Ni of 3/2. This suggests that La3Ni207 is, at least at 1100 “C, a metastable phase.
219
References 1 2 3 4 5 6 7 8 9
A. Wold, B. Post and E. Banks, J. Am. Chem. Sot., 79 (1957) 4911. A. Rabenau and P. Eckerlin, Acta Crystallogr., 11 (1958) 304. J. Sieler and J. Kaiser, Z. Anorg. Allg. Chem., 377 (1970) 316. A. Wold and R. J. Amott, J. Phys. Chem. Solids, 9 (1959) 176. M. Arjomand and D. J. Machin, J. Chem. Sot., Dalton Trans., (1975) 1055. T. Nakamura, G. Petzow and L. J. Gauckel, Mater. Res. Bull., 14 (1979) 649. M. Seppiinen and M. G. Tikkanen, Acta Chem. Stand.. Ser. A, 30 (1979) 389. J. J. Janacek and G. P. Wirtz, J. Am. Ceram. Sot., 61 (1978) 342. F. Abbattista, M. Vallino and C. Brisi, Atti Accad. Sci. Torino, Cl. Sci. Fis., Nat. Mat., 114 (1980). 10 S. N. Ruddlesden and P. Popper, Acta Crystallogr., 11 (1958) 54.