Journal of Materials Chemistry A View Article Online
PAPER
View Journal | View Issue
Downloaded by University of Sydney on 12 February 2013 Published on 10 January 2013 on http://pubs.rsc.org | doi:10.1039/C3TA00540B
Cite this: J. Mater. Chem. A, 2013, 1, 3127
Received 3rd October 2012 Accepted 9th January 2013
Synthesis, structures and properties of transition metal doped SrIrO3† Ilyas Qasim,a Brendan J. Kennedy*a and Maxim Avdeevb The synthesis of some transition metal SrIr1xMxO3 type oxides is described. These have an orthorhombic perovskite type-structure and are only found when the formal oxidation state of the Ir is approximately equal to +4.5 and for M ¼ Fe, Co, Ni and Zn. Occupancy of the TM eg type orbitals appears to contribute to the break-down of the dimeric motif seen in the 6H–SrIrO3 structure. Variable
DOI: 10.1039/c3ta00540b
temperature resistivity measurements show that SrIr0.8Zn0.2O3 is a metal; SrIr0.8Ni0.2O3 an non-metal and
www.rsc.org/MaterialsA
SrIr0.8Co0.2O3 undergoes a temperature dependent metal–insulator transition.
1
Introduction
Transition-metal oxides containing the 4d or 5d metals, Mo–Rh and W–Ir are of considerable current interest since these oen exhibit cooperative quantum phenomena due to competition between Coulombic repulsion and the itinerancy of d electrons. Ru and Ir oxides typically show high electronic conductivity due to the size of the nd orbitals, although there are numerous exceptions including the Mott insulator Sr2IrO4. The unique behaviour of Sr2IrO4 is driven by the large spin–orbit coupling of the 5d orbitals.1,2 Despite the chemical similarity of Ru and Ir there are numerous examples where the properties of the corresponding oxides are remarkably different. Sr2RuO4 has a similar layered structure to Sr2IrO4 (ref. 3) and is a rare example of a 4d superconductor.4,5 The impact of chemical doping of such oxides is considerable current interest.6,7 A further illustration of the differences between Ru and Ir is seen in the ABO3 perovskites. SrRuO3 is an unusual example of a ferromagnetic 4d metal oxide.8 It is isostructural with CaTiO3, both adopting the orthorhombic Pbnm-type structure at room temperature.9,10 Conversely SrIrO3 is a paramagnetic metal and, as rst reported by Longo and co-workers in 1971,11 adopts a monoclinic distortion of the hexagonal BaTiO3 type structure, in space group C2/c, when prepared at ambient pressure. This structure transforms to the orthorhombic Pbnm structure when heated to 1000 C at 40 kbar. The orthorhombic form of SrIrO3 (O–SrIrO3) is paramagnetic and undergoes a metal–insulator transition near 44 K.11 Since the discovery of ferromagnetism in SrRuO3 there has been considerable effort to tune its magnetic properties a
School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia. E-mail:
[email protected]; Fax: +61 2 9351 3329; Tel: +61 2 9351 2742
b
Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales, 2234, Australia † Electronic supplementary 10.1039/c3ta00540b
information
(ESI)
available.
This journal is ª The Royal Society of Chemistry 2013
See
DOI:
through substitution of either the Sr or Ru cations.12–17 Almost without exception such doping leads to a lowering of the Curie temperature, the Cr doped oxides, SrRu1xCrxO3, being the notable outlier.13,18,19 In contrast to the extensive literature on the effect of chemical doping on SrRuO3 very few studies have described the role of chemical substitution on the structure and properties of SrIrO3. Introducing other transition metal into the Ir-site should be a promising approach to develop new materials. In the present work we describe efforts to synthesise oxides of the type of SrIr1xMxO3 where M is a rst row transition metal. This has lead to the preparation of a number of new oxides and the structures and magnetic properties of these are described. This work considerably expands the recent report of Bremholm et al. who describe the use of Zn and Li to destabilize the monoclinic SrIrO3 structure.20
2
Experimental
Polycrystalline samples of SrIrO3 and SrIr1xMxO3 (M ¼ 3d transition metal, 0 # x # 2/3) were synthesized by solid state reaction methods, using stoichiometric quantities of SrCO3 (99.99% Aldrich), Ir metal (99.99% Aithaca), TiO2, V2O5, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, CuO and ZnO. The transition metal oxides were from Aldrich and of purity $99.99% except for Fe2O3 that was 99% pure. These powders were mixed, ground and preheated in alumina crucibles at 800 C for 12 h. Successive grinding, pelletizing and heating were performed at 1000 C and 1100 C for 48 h, and nally in temperature range 1120 C to 1180 C, until the diffraction pattern no longer changed or the sample had no detectable impurities. All reactions were monitored by powder X-ray diffraction with Cu Ka radiation, using a PANalytical X'Pert PRO X-ray diffractometer equipped with a PIXcel solid-state detector. Variable temperature measurements were undertaken on the same diffractometer using a XRK 900 Reactor Chamber. For such measurements
J. Mater. Chem. A, 2013, 1, 3127–3132 | 3127
View Article Online
Downloaded by University of Sydney on 12 February 2013 Published on 10 January 2013 on http://pubs.rsc.org | doi:10.1039/C3TA00540B
Journal of Materials Chemistry A
Paper
the sample was allowed to equilibrate for ve minutes aer reaching each the desired temperature. Each pattern took around 18 minutes to collect. Synchrotron X-ray powder diffraction data were collected using the powder diffractometer at beamline BL-10 of the Australian Synchrotron.21 The sample was nely ground and housed in a sealed 0.2 mm diameter quartz capillary that was rotated during the measurements. The wavelength was set ˚ and the precise value of this was determined using at 0.825 A, a NIST LaB6 standard reference material. Neutron diffraction data for SrIrO3 and SrIr0.8Ni0.2O3 were collected at room temperature over the angular range 10 < 2q < 162 with ˚ using the high resoneutrons of wavelength 2.439 or 1.622 A, lution powder diffractometer Echidna at the Australian Nuclear Science and Technology Organisation's OPAL facility.22 The X-ray diffraction data was used to rene the structures by the Rietveld method as implemented in the program RIETICA.23 The peak shapes were modelled using a pseudo Voigt function and the background was estimated by interpolating between, up to, 40 selected points. The scale factor, detector zero point, lattice parameters, atomic coordinates and atomic displacement parameters were rened together with the peak prole parameters. The site occupancy factors of the cations were xed to the nominal values. The structural renements from the neutron diffraction data used GSAS.24 The oxygen content of the samples, estimated from the neutron diffraction measurements, suggested full occupancy of the oxygen sites. Magnetic properties and electrical resistivity of the materials were measured with a Quantum Design Physical Property Measurement System (PPMS) system in the range of 5–300 K. Zero-eld cooled (ZFC) and eld-cooled (FC) magnetic susceptibility data were collected with a magnetic eld of 1000 Oe.
3
Results and discussion
3.1
SrIr1xMxO3 solid solutions
Our efforts to prepare samples of the type SrIr1xMxO3 with various transition metals (M) at ambient pressure are summarised in Table 1. It was established from these experiments that attempts to substitute Ir with another metal rarely resulted in the formation of single phase materials. With notably few exceptions the 6H–SrIrO3 structure persisted when the M dopant level was between 5 and 20%, however the diffraction
Table 1 Summary of attempted synthesis of compositions in the series SrIr1xMxO3. Unsuccessful syntheses are indicated by the crosses. Where the entry is blank the composition was not investigated
x/M
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
0.10 0.15 0.20 0.25 0.30 0.33 0.50 0.66
7
7
7
7
7
7 7 7 7
7
7
7
7
7
7 7 3 x ¼ 0.22 7
7 7 7 7
7 7 3 3 7 7
7
7
7
7 7 7
7 7 7 3 3 3
7 7 3 3 7
3128 | J. Mater. Chem. A, 2013, 1, 3127–3132
Ga
7 7 7
patterns revealed the presence of at least two phases. For none of the metals investigated was it possible to obtain single phase samples of the composition SrIr0.9M0.1O3, although examination of the diffraction pattern suggested the formation of a regular perovskite type structure at ambient pressure was possible. For M ¼ Co, Ni or Zn increasing the dopant level to x ¼ 0.2 yielded single phase samples. Analysis of the X-ray diffraction patterns from these three samples demonstrated that products had the orthorhombic distortion of the ABO3 perovskite structure found in SrRuO3. The same orthorhombic structure was found where the amount of Co, Ni or Zn was increased to 0.25. Increasing the transition metal content to greater values resulted in the appearance of additional reections in the diffraction patterns indicative of impurity phases. Attempts to prepare single phase SrIr0.8M0.2O3 (M ¼ Ti, V, Cr, Mn, Fe or Cu) samples were invariably unsuccessful, although for M ¼ Fe single phase samples were formed for x ¼ 0.33–0.66. The size of the cation appears to contribute to the stability of the doped oxides, in general cations with ionic radii smaller than that of Ir4+ (0.625 ˚ tended not to form single phase orthorhombic perovskites A) whereas dopant cations with ionic radii greater than that of Ir4+ were more likely to form single phase materials. This observation is in contrast with the suggestion of Bremholm et al.,20 that there is no obvious correlation between the ionic size of the dopant cation and the formation of the orthorhombic perovskite. We concur with Bremholm et al.20 that the effective size of the B-site cation is relatively unimportant. Our synthetic efforts, summarised in the Table 1, demonstrated that single phase samples could only be obtained with very specic x values, x ¼ 0.2–0.25 for divalent metals and 0.33 $ x $ 0.66 for trivalent metals. Lower or higher values always resulted in mixed phase samples. It is postulated that a critical role of the substituting M is to increase the average effective oxidation state of iridium from +4 to at least +4.5. It is intriguing that the specic conditions for the formation of SrIr1xMxO3 solid solution series involves Ir4.5+, where Ir4+ and Ir5+ must be present in 1 : 1 ratio as SrIr0.44+Ir0.45+M0.22+O3 and SrIr0.334+Ir0.335+M0.333+O3. From this very specic ratio, it is tempting to propose that B-cation ordering occurs, however we nd no evidence of long range ordering in the diffraction measurements. An increase in the formal oxidation state of the Ir to +4.5 alone is an insufficient condition to destabilise the dimeric Ir2 motif of the 6H–SrIrO3 structure; such Ir4.5+ dimers are observed in oxides such as Ba3LnIr2O9 (ref. 25) and Ba3BiIr2O9,26 where Ln is a trivalent lanthanoid. Indeed the same face sharing Ir2 motif is found in Ba3CaIr2O9 (ref. 27) that contains Ir5+. In a similar fashion to that seen for SrIrO3 the face sharing motif in Ba3CaIr2O9 is destabilised at high pressure where an ordered corner sharing structure forms.28 In general the Ba3MIr2O9 oxides are isostructural with 6H–SrIrO3 where the M-type cations are ordered on corner sharing octahedral sites and the Ir exclusively occupies the face sharing sites.25,26 Nevertheless the formal oxidation state of the Ir appears to be an important contribution in destabilising the 6H–SrIrO3 structure. One obvious difference between the current SrIr1xMxO3 oxides and
This journal is ª The Royal Society of Chemistry 2013
View Article Online
Downloaded by University of Sydney on 12 February 2013 Published on 10 January 2013 on http://pubs.rsc.org | doi:10.1039/C3TA00540B
Paper the well studied Ba analogues, Ba3MIr2O9, is the disorder of the transition metal ion at the Ir sites. We believe that the presence of the transition metal ion at the face sharing sites is the main driving force in breaking down the stable Ir–Ir bonding in Ba3MIr2O9. The formation of perovskite-type structures appears to be dependent on the d-electron conguration of the metals. Doping SrIrO3 with Fe, Co, Ni and Zn results in the formation of a single phase perovskites, albeit at different dopant levels. Each of these metals contains electrons in the eg orbitals whereas the earlier transition metals (Ti, V and Cr) do not. Mn and Cu are an exception to this trend and, although we have not unequivocally established the formal oxidation states of these, our inability to prepare single phase samples containing Cu2+ or Mn3+ possibly reects the inuence of a Jahn–Teller (JT) type distortion for these cations. Both Cu2+ and Mn3+ can be incorporated into SrRuO3, although the presence of the JT active cation is accompanied by a transition to a tetragonal structure.15,29 Since both Zn2+ and Ga3+ have a d10 electron conguration we explored the possibility of preparing samples of the type SrIr1xGaxO3 for x ¼ 0.2, 0.33, 0.5, however we were unable to isolate single phase samples. Likewise attempts to introduce Al into SrIrO3 were unsuccessful. We note that Pi and co-workers14 reported that Al3+ and Ga3+ could not be substituted for Ru in SrRuO3. 3.2 Crystal structure of SrIrO3 and its temperature dependence SrIrO3 adopts a monoclinic distortion of the 6H-hexagonal perovskite structure when prepared at ambient pressure. In this structure there are two independent positions for the Ir atoms. At both sites the Ir cations are coordinated to six oxygen anions and the Ir(2)O6 octahedra are arranged as pairs of face-shared octahedra that are joined by common corners to a plane of corner sharing Ir(1)O6 octahedra, see Fig. 1(a). The structure was rened from neutron diffraction data (Fig. 2) in
Fig. 1 Representation of the crystal structure of (a) SrIrO3 and (b) SrIr0.8Ni0.2O3. The former structure is characterised by face sharing Ir2 dimers that are absent in the latter structure.
This journal is ª The Royal Society of Chemistry 2013
Journal of Materials Chemistry A
Fig. 2 Observed, calculated and difference (a) synchrotron X-ray diffraction and (b) powder neutron diffraction patterns for SrIrO3 at room temperature.
space group C2/c and the rened structural parameters are summarised in Table 2. In this structure the Ir(1) cation has an ˚ typical of Ir4+ with the indiaverage Ir–O distance of 2.006 A ˚ In vidual distances in a narrow range 1.987(7)–2.038(8) A. contrast the Ir(2) octahedra in the Ir2O9 dimers are not regular. The Ir(2)–O(1) bond lengths, on the shared face of the dimer,
Table 2 (a) Structural parameters for SrIrO3. The structure was refined, from neutron diffraction data, in space group C2/c (no. 15) with a ¼ 5.60401(29), b ¼ ˚ b ¼ 93.202(4) and vol. ¼ 763.89(6) A ˚ 3. (b) Selected 9.6256(4), c ¼ 14.1834(7) A, ˚ bond lengths (A) and angles ( ) for SrIrO3
Name
Site
x
y
z
Uiso 100
Sr1 Sr2 Ir1 Ir2 O1 O2 O3 O4 O5
4e 8f 4a 8f 4e 8f 8f 8f 8f
0 0.0122(10) 0 0.9820(8) 0 0.2411(14) 0.8112(13) 0.9407(15) 0.3238(18)
0.0092(10) 0.6667(8) 0 0.6660(5) 0.4981(13) 0.2649(7) 0.4077(8) 0.1544(9) 0.4204(8)
0.25 0.0957(4) 0 0.84698(29) 0.25 0.2630(5) 0.0474(5) 0.4087(5) 0.1058(6)
2.85(22) 4.82(20) 4.78(20) 4.59(14) 5.84(39) 2.87(19) 5.72(24) 5.35(29) 5.86(23)
˚) Ir1–O3 2 (A ˚) Ir1–O4 2 (A ˚ Ir1–O5 2 (A) ˚ Ir1–O (average) (A) ˚) Ir2–O1 (A ˚) Ir2–O2 (A ˚ Ir2–O2 (A) ˚ Ir2–O3 (A) ˚) Ir2–O4 (A ˚) Ir2–O5 (A ˚ Ir2–O (average) (A) ˚ Ir2–Ir2 (A) Ir2–O3–Ir1 ( ) Ir2–O4–Ir1 ( ) Ir2–O5–Ir1 ( ) Ir2–O–Ir1 (average) ( ) Ir2–O1–Ir2 ( ) Ir2–O2–Ir2 2 ( ) Ir2–O–Ir2 (average) ( )
2.038(8) 1.987(7) 1.994(7) 2.006 2.100(11) 2.055(8) 2.040(8) 1.974(9) 1.957(9) 2.051(9) 2.030 2.770(8) 149.6(4) 158.8(5) 149.3(5) 152.6 82.5(6) 85.11(31) 84.2
J. Mater. Chem. A, 2013, 1, 3127–3132 | 3129
View Article Online
Downloaded by University of Sydney on 12 February 2013 Published on 10 January 2013 on http://pubs.rsc.org | doi:10.1039/C3TA00540B
Journal of Materials Chemistry A are longer than those to O(2) that are on the vertices of the ˚ is also Ir(2)O6 octahedra. The average Ir(2)–O distance 2.030 A 30 typical of tetravalent Ir. The Ir(2)–Ir(2) distances is relatively ˚ but is noticeably longer the Ir–Ir distance short, 2.770(8) A, found in the members of the series Ba3Ln3+Ir24.5+O9 (Ir–Ir ˚ 31 reecting the greater electrostatic distance 2.53–2.58 A), repulsion of the Ir4.5+ dimers. Variable temperature X-ray powder diffraction measurements conrmed that the monoclinic C2/c structure of SrIrO3 is stable up to 900 C, and no evidence for any structural phase transitions was evident in these measurements. The thermal expansion of the material is unremarkable and although the monoclinic angle is systematically reduced upon heating it is evident that a transition to the hexagonal structure will not occur below the decomposition temperature of SrIrO3. These results are in good agreement with that reported by Longo and co-workers11 and are summarised in the ESI.† 3.3 Crystal structures of SrIr1xMxO3 and their temperature dependence The partial replacement of the Ir with selected 3d transition metals in SrIr1xMxO3 results in a break down the Ir–Ir bond observed in the 6H-hexagonal structures and stabilized the corner shared octahedral arrangement of the orthorhombic GdFeO3 structure in space group Pbnm see Fig. 1(b). The structure of one example, SrIr0.8Ni0.2O3, was investigated using neutron diffraction along with synchrotron X-ray diffraction (Fig. 3) and these data allowed us to obtain an accurate description of the structure that had rened lattice parameters ˚ at room of a ¼ 5.5938(2), b ¼ 5.5571(2) and c ¼ 7.8835(2) A temperature. In the orthorhombic structure there are two anion sites. The occupancies of the two oxygen sites were rened and no evidence for any oxygen vacancies was obtained suggesting the material to be stoichiometric. The rened structural parameters are given in Table 3. The Ni and Ir are disordered on the same site and are located at the centre of a slightly distorted ˚ There are two different octahedron with 2 M–O(1) at 1.997(1) A.
Paper ˚ The average M–O M–O(2) distances 1.997(26) and 2.003(2) A. ˚ distance in SrIr0.8Ni0.2O3 of 1.999 A is essentially the same as the Ir–O distances seen in 6H–SrIrO3. The structures of the remaining oxides were estimated from renements against X-ray diffraction data (see ESI† for gures). As a consequence of the large X-ray scattering power of the heavy Ir cations, the precision of these renements is relatively low. Nevertheless the rened distances seem reasonable and suggest that the doping cation does not signicantly distort the MO6 octahedra. Variable temperature X-ray measurements of the samples listed in Table 3 were undertaken and these demonstrated that the materials transformed to a cubic structure when heated above 700 C. Studies are ongoing to conrm that the sequence of structures is the same as that found in SrRuO3.10 In all cases there is evidence for the formation of an intermediate tetragonal structure in I4/mcm. Variable temperature neutron diffraction measurements are required to establish accurate structures of these oxides at high temperatures.
4
Physical properties of SrIr1xMxO3
4.1
Magnetism
Zero-eld cooled and eld-cooled magnetization curves for selected single phase samples are given in Fig. 4. These measurements conrm that 6H–SrIrO3 is a Pauli paramagnet and reveal SrIr0.8Ni0.2O3 to be a paramagnet with Curie–Weiss type behaviour. There is noticeable branching of the ZFC and FC magnetic susceptibility curves for both the Co and Zn doped oxides. The susceptibility measurements suggest a ferromagnetic transition near 240 K occurs in SrIr0.8Zn0.2O3. Sr2IrO4 is ferromagnetic with Tc 240 K.32 It is possible that the behaviour of SrIr0.8Zn0.2O3 is the result of a small amount Sr2IrO4 forming in the sample. Although the diffraction measurements show no evidence for such impurities, the magnetic measurements are expected to be considerably more sensitive to ferromagnetic impurities. Since it was possible to prepare SrIr0.75Zn0.25O3 the magnetic properties of this were also investigated and this is also weakly ferromagnetic with a similar transition temperature, supporting the idea that the observed ferromagnetism is not intrinsic to the material. The low temperature magnetic behaviour of SrIr0.8Co0.2O3 appears typical of a spin-glass, and there is no evidence for long range magnetic ordering. 4.2
Fig. 3 Observed, calculated and difference patterns of room temperature (a) synchrotron X-ray diffraction and (b) powder neutron diffraction data for SrIr0.8Ni0.2O3.
3130 | J. Mater. Chem. A, 2013, 1, 3127–3132
Electrical resistivity
The temperature dependence of electrical resistivity in the range of 4–300 K for the three orthorhombic SrIr0.8M0.2O3 perovskites is compared with that of undoped 6H–SrIrO3 in Fig. 5. Whereas 6H–SrIrO3 is a metal over this temperature range, the behaviour of each of the three orthorhombic samples is somewhat different. The Zn doped sample is still metallic with the resistivity being only weakly temperature dependent. Conversely SrIr0.8Ni0.2O3 is a semi-conductor with the resistivity increasing as the temperature is lowered. In the case of M ¼ Co a metal–insulator transition (MIT) temperature is observed with
This journal is ª The Royal Society of Chemistry 2013
Downloaded by University of Sydney on 12 February 2013 Published on 10 January 2013 on http://pubs.rsc.org | doi:10.1039/C3TA00540B
View Article Online
Paper
Journal of Materials Chemistry A
Table 3 data
Structural parameters and refinement details for SrIr1xMxO3 refined in SG Pbnm from synchrotron-XRD. The results for SrIr0.8Ni0.2O3 used neutron diffraction
˚) a (A ˚ b (A) ˚ c (A) ˚ 3) Vol. (A Rp Rwp c2 ˚) Ir/M–O1 A ˚) Ir/M–O2 (A ˚ Ir/M–O2 (A) Ir–O (avg.) O1–Ir–O2 ( ) O1–Ir–O2 ( ) O2–Ir–O2 ( )
SrIr0.8Co0.2 O3
SrIr75Co0.25O3
SrIr0.8Ni0.2O3
SrIr0.78Ni0.22O3
SrIr0.8Zn0.2O3
SrIr0.75Zn0.25O3
5.59690(7) 5.56230(7) 7.88542(11) 245.49(1) 2.43 3.19 7.1 2.045(6) 2.053(10) 1.934(9) 2.011 99.3(7) 95.2(7) 90.81(4)
5.59310(6) 5.55810(6) 7.88119(9) 245.00(5) 2.21 2.79 2.11 1.982(2) 2.04(2) 1.97(2) 1.997 92.9(8) 92.2 (7) 91.6(2)
5.5938(2) 5.5571(2) 7.8835 (2) 245.1(1) 5.02 6.55 1.88 1.997(7) 2.003(3) 1.997(3) 1.999 90.4(2) 90.0(2) 91.2(3)
5.59379(6) 5.55875(6) 7.88438(8) 245.16(1) 2.29 2.92 2.31 1.982(3) 2.05(1) 1.94(1) 1.991 90.7(9) 96.0(8) 90.9(7)
5.60950(6) 5.58010(6) 7.90960(9) 247.58(5) 2.11 2.68 5.30 2.026(4) 2.001(7) 2.014(6) 2.013 95.9(8) 93.08(7) 90.58(7)
5.58071(9) 5.60929(9) 7.90649(13) 247.50(4) 2.19 2.82 2.63 2.058(5) 1.99(10) 1.99(9) 2.013 99.4(7) 100.2(9) 90.42(8)
in the c–T curve for SrIr0.8Co0.2O3 at TMI strongly suggests that the MIT transition is not associated with a change in the magnetic ordering. The magnetic transition observed for SrIr0.8Co0.2O3 near T* (170 K, Fig. 4) does not have an analogous feature in the r–T curve. Using slightly different synthetic protocols Bremholm and co-workers20 prepared SrIr0.75Zn0.25O3 and SrIr0.67Zn0.33O3. The resistivity of these was found to increase upon cooling to low temperatures, showing them to be semiconductors, whereas we nd the less heavily doped oxide SrIr0.8Zn0.2O3 to be metallic. The transition from metal to insulator is consistent with the conclusion of these authors that these oxides display Mott variable range hopping type behaviour, with increasing disorder reducing the conductivity. Fig. 4 Temperature dependence of magnetization for SrIr0.8M0.2O3 samples recorded with an applied magnetic field of 1000 Oe.
TMI about 70 K. This is somewhat higher than TMI ¼ 44 K reported for pure O–SrIrO3. There is no evidence for a MIT in either the Ni or Zn doped samples. The absence of any anomaly
5
Conclusion
The 6H-type SrIrO3 is found to be remarkably intolerant to doping by transition metals to form SrIr1xMxO3 type oxides. Exceptions are found when the formal oxidation state of the Ir is approximately equal to +4.5 with single phase oxides found for M ¼ Fe, Co, Ni and Zn. Occupancy of the TM eg type orbitals orbitals appears to contribute to the break-down of the dimeric motif seen in the 6H–SrIrO3 structure. The size of the dopant cation also appears to be important and single phase oxides were only formed when the doptant cations had a larger ionic radii than that of Ir4+. The electronic and magnetic properties of the oxides are extremely sensitive to the dopant cation. Whereas SrIr0.8Zn0.2O3 is a metal and SrIr0.8Ni0.2O3 an non-metal, the analogous Co oxide SrIr0.8Co0.2O3 undergoes a temperature dependent metal–insulator transition.
Acknowledgements Fig. 5 Temperature dependence of the resistivity for SrIr0.8M0.2O3 samples. Note the use of the logarithmic scale.
This journal is ª The Royal Society of Chemistry 2013
BJK acknowledges the support of the Australian Research Council. This work was, in part, performed at the powder diffraction beamline at the Australian Synchrotron.
J. Mater. Chem. A, 2013, 1, 3127–3132 | 3131
View Article Online
Journal of Materials Chemistry A
Downloaded by University of Sydney on 12 February 2013 Published on 10 January 2013 on http://pubs.rsc.org | doi:10.1039/C3TA00540B
References 1 B. J. Kim, H. Jin, S. J. Moon, J. Y. Kim, B. G. Park, C. S. Leem, J. Yu, T. W. Noh, C. Kim, S. J. Oh, J. H. Park, V. Durairaj, G. Cao and E. Rotenberg, Phys. Rev. Lett., 2008, 101, 076402. 2 B. J. Kim, H. Ohsumi, T. Komesu, S. Sakai, T. Morita, H. Takagi and T. Arima, Science, 2009, 323, 1329–1332. 3 Q. Huang, J. L. Soubeyroux, O. Chmaissem, I. Natalisora, A. Santoro, R. J. Cava, J. J. Krajewski and W. F. Peck, J. Solid State Chem., 1994, 112, 355–361. 4 Y. Maeno, H. Hashimoto, K. Yoshida, S. Nishizaki, T. Fujita, J. G. Bednorz and F. Lichtenberg, Nature, 1994, 372, 532–534. 5 S. B. Chung, S. Raghu, A. Kapitulnik and S. A. Kivelson, Phys. Rev. B: Condens. Matter Mater. Phys., 2012, 86, 064525. 6 J. M. Carter, V. V. Shankar, M. A. Zeb and H. Y. Kee, Phys. Rev. B: Condens. Matter Mater. Phys., 2012, 85, 115105. 7 A. P. Mackenzie and Y. Maeno, Rev. Mod. Phys., 2003, 75, 657–712. 8 A. Callaghan, C. W. Moeller and R. Ward, Inorg. Chem., 1966, 5, 1572. 9 B. J. Kennedy, C. J. Howard and B. C. Chakoumakos, J. Phys.: Condens. Matter, 1999, 11, 1479–1488. 10 B. J. Kennedy, B. A. Hunter and J. R. Hester, Phys. Rev. B: Condens. Matter Mater. Phys., 2002, 65, 224103. 11 J. M. Longo, J. A. Kafalas and R. J. Arnott, J. Solid State Chem., 1971, 3, 174. 12 G. Cao, S. McCall, M. Shepard, J. E. Crow and R. P. Guertin, Phys. Rev. B: Condens. Matter Mater. Phys., 1997, 56, 321–329. 13 B. Dabrowski, S. Kolesnik, O. Chmaissem, T. Maxwell, M. Avdeev, P. W. Barnes and J. D. Jorgensen, Phys. Rev. B: Condens. Matter Mater. Phys., 2005, 72, 054428. 14 L. Pi, A. Maignan, R. Retoux and B. Raveau, J. Phys.: Condens. Matter, 2002, 14, 7391–7398. 15 B. J. Kennedy and Q. Zhou, Solid State Commun., 2008, 147, 208–211. 16 I. Qasim, B. J. Kennedy, Z. M. Zhang, M. Avdeev and L. Y. Jang, J. Phys.: Condens. Matter, 2011, 23, 435401. 17 R. A. Ricciardo, H. L. Cuthbert, P. M. Woodward, Q. D. Zhou, B. J. Kennedy, Z. M. Zhang, M. Avdeev and L. Y. Jang, Chem. Mater., 2010, 22, 3369–3382.
3132 | J. Mater. Chem. A, 2013, 1, 3127–3132
Paper 18 Z. H. Han, J. I. Budnick, W. A. Hines, B. Dabrowski, S. Kolesnik and T. Maxwell, J. Phys.: Condens. Matter, 2005, 17, 1193–1200. 19 A. J. Williams, A. Gillies, J. P. Atteld, G. Heymann, H. Huppertz, M. J. Martinez-Lope and J. A. Alonso, Phys. Rev. B: Condens. Matter Mater. Phys., 2006, 73, 104409. 20 M. Bremholm, C. K. Yim, D. Hirai, E. Climent-Pascual, Q. Xu, H. W. Zandbergen, M. N. Ali and R. J. Cava, J. Mater. Chem., 2012, 22, 16431–16436. 21 K. S. Wallwork, B. J. Kennedy and D. Wang, AIP Conf. Proc., 2007, 879, 879–882. 22 K. D. Liss, B. Hunter, M. Hagen, T. Noakes and S. Kennedy, Phys. B, 2006, 385–386, 1010–1012. 23 B. A. Hunter and C. J. Howard, RIETICA A Computer Program for Rietveld Analysis of X-Ray and Neutron Powder Diffraction Patterns, 1998. 24 A. C. Larson and R. B. von Dreele, General Structure Analysis System (GSAS), Los Alamos National Laboratory, Report No LAUR 86-748, 2000. 25 Y. Doi and Y. Hinatsu, J. Phys.: Condens. Matter, 2004, 16, 2849–2860. 26 W. Miiller, M. Avdeev, Q. D. Zhou, B. J. Kennedy, N. Sharma, R. Kutteh, G. J. Kearley, S. Schmid, K. S. Knight, P. E. R. Blanchard and C. D. Ling, J. Am. Chem. Soc., 2012, 134, 3265–3270. 27 T. Sakamoto, Y. Doi and Y. Hinatsu, J. Solid State Chem., 2006, 179, 2595–2601. 28 J. G. Zhao, L. X. Yang, Y. Yu, F. Y. Li, R. C. Yu and C. Q. Jin, J. Solid State Chem., 2009, 182, 327–330. 29 R. Nithya, S. Chandra, M. C. Valsakumar, V. S. Sastry, T. C. Han and J. G. Lin, J. Appl. Phys., 2007, 102, 013512. 30 A. A. Bolzan, C. Fong, B. J. Kennedy and C. J. Howard, Acta Crystallogr., Sect. B: Struct. Sci., 1997, 53, 373–380. 31 Y. Doi and Y. Hinatsu, J. Solid State Chem., 2004, 177, 3239– 3244. 32 G. Cao, J. Bolivar, S. McCall, J. E. Crow and R. P. Guertin, Phys. Rev. B: Condens. Matter Mater. Phys., 1998, 57, 11039– 11042.
This journal is ª The Royal Society of Chemistry 2013
