Crystal Structures and Properties of Perovskites ScCrO3 and InCrO3

May 18, 2012 - National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. •S Supporting ... Antiferromagnetic ...
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Crystal Structures and Properties of Perovskites ScCrO3 and InCrO3 with Small Ions at the A Site Alexei A. Belik,*,† Yoshitaka Matsushita,‡ Masahiko Tanaka,‡ and Eiji Takayama-Muromachi§ †

International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan ‡ SPring-8 Office, National Institute for Materials Science (NIMS), Kohto 1-1-1, Sayo-cho, Hyogo 679-5148, Japan § National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan S Supporting Information *

ABSTRACT: ScCrO3 and InCrO3 were synthesized at high pressure of 6 GPa and 1500 K. Crystal structures of ScCrO3 and InCrO3 were studied with synchrotron X-ray powder diffraction. They crystallize in the GdFeO3-type perovskite structure (space group Pnma, a = 5.35845(1) Å, b = 7.37523(1) Å, c = 5.03139(1) Å for ScCrO3 and a = 5.35536(1) Å, b = 7.54439(1) Å, c = 5.16951(1) Å for InCrO3). The physical properties of ScCrO3 and InCrO3 were investigated with specific heat, ac/dc magnetization, and dielectric measurements and compared with those of YCrO3 with nonmagnetic Y3+ ions at the A site. Antiferromagnetic transitions occur at TN = 73 K in ScCrO3 and 93 K in InCrO3 in agreement with the general trend of ACrO3 (A = Y and rare earths) where TN decreases with decreasing the radius of the A ions. Extremely weak ferromagnetism was found in ScCrO3 and InCrO3 in contrast to YCrO3. Ac magnetization measurements revealed some peculiarities in behavior of ScCrO3 and InCrO3, namely, double-peak anomalies just below TN. Dielectric anomalies were observed in both compounds at TN indicating magnetoelectric coupling in contact with YCrO3 where no dielectric anomalies were found. ScCrO3 and InCrO3 are very stable for high-pressure phases: no decomposition of ScCrO3 was observed after heating up to 1340 K in air, and InCrO3 only partially decomposed at 1340 K to give Cr2O3 and ambient- and high-pressure modifications of In2O3 as impurities. No anomalies were also found with differential scanning calorimetry up to 870 K and differential thermal analysis up to 1340 K, indicating the absence of hightemperature phase transitions. KEYWORDS: perovskites, cromites, multiferroics, high-pressure

1. INTRODUCTION Perovskite-type compounds with the general formula ABO3, where A is La−Lu and Y and B is V, Cr, Mn, Fe, Co, Ni, and Cu, have been attracting a lot of attention for decades. For example, LaMnO3 and its derivatives have been extensively studied in relation to the colossal magnetoresistance effect and orbital/charge orderings.1,2 AVO3 and ANiO3 are interesting because of orbital/charge orderings3,4 and LaCoO3 because of the unusual spin state of Co3+.5,6 The doped LaCrO3 is a good oxygen-ion conductor.7 The discovery of multiferroic properties in ACrO3 and AMnO3 attracted renewed attention to these systems.8−12 ACuO3‑δ (A = La and Nd)13,14 shows rich crystallochemistry depending on the oxygen content. “Exotic” perovskites are also highly interesting because new phenomena may emerge in them. The term “exotic” may include compounds with unusual oxidation states (e.g., Bi0.53+Bi0.55+Ni2+O3 and Ba2Bi3+Bi5+O6),15,16 unusual ion distribution (e.g., (In1−xMnx)MnO3 with 0.111 ≤ x ≤ 0.333),17 and unusual ions at the A site (e.g., ScVO3 with small Sc3+ ions)18 and B site (e.g., SrTcO3).19 Interesting © 2012 American Chemical Society

properties were really observed in them. For example, ScVO3 shows a highly stable Jahn−Teller distortion and different structural and magnetic properties in comparison with other members of the AVO3 family;18 SrTcO3 has an extraordinarily high Néel temperature of 1023 K;19 BiNiO3 and Bi1−xLaxNiO3 show a pressure-induced and temperature-induced intermetallic charge transfer and large negative expansion during these transitions;15 and Ba1−xKxBiO3 is a superconductor.20 Only seven examples of “exotic” perovskites with small In3+ and Sc3+ ions at the A site are know today: ScCrO3,21 ScAlO3,22 ScVO3,18 InCrO3,23 InRhO3,23 and (In1−xMx)MO3 (M = Mn and Fe0.5Mn0.5).17,24,25 All of them require high-pressure hightemperature conditions for the preparation. At ambient pressure, different structure types are formed.26,27 For example, InFeO3,28 ScMnO3,29 InMnO3,29,30 and InCu2/3V1/3O331 have YAlO3-type or LuMnO3-type hexagonal structures; and Received: March 22, 2012 Revised: May 17, 2012 Published: May 18, 2012 2197

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Table 1. Structure Parameters of ScCrO3 and InCrO3 at Room Temperaturea site

Wyckoff position

x

Sc Cr O1 O2

4c 4b 4c 8d

0.07206(7) 0 0.4400(3) 0.3104(2)

In Cr O1 O2

4c 4b 4c 8d

0.05868(4) 0 0.4394(4) 0.3067(3)

y

z

B (Å2)

0.25 0 0.25 0.06773(14)

0.97772(9) 0.5 0.1349(3) 0.6816(2)

0.367(7) 0.247(6) 0.19(2) 0.42(2)

0.25 0 0.25 0.06551(19)

0.98311(5) 0.5 0.1257(3) 0.6885(3)

0.277(5) 0.144(9) 0.19(3) 0.44(3)

ScCrO3

InCrO3

a The occupation factor of all sites is unity. Space group Pnma (No 62); Z = 4. ScCrO3: a = 5.35845(1) Å, b = 7.37523(1) Å, c = 5.03139(1) Å, and V = 198.8398(4) Å3; Rwp = 6.07%, Rp = 3.82%, RB = 4.11%, and RF = 2.06%; the weight fraction of Cr2O3 is 0.6%. ρcal = 4.842 g/cm3. InCrO3: a = 5.35536(1) Å, b = 7.54439(1) Å, c = 5.16951(1) Å, and V = 208.8633(7) Å3; Rwp = 4.56%, Rp = 3.33%, RB = 3.21%, and RF = 1.88%; the weight fraction of Cr2O3 is 1.3%. ρcal = 6.831 g/cm3.

ScVO3,18 ScFeO3,32 InVO3,33 and In2RuFeO634 have bixbyitetype cubic structures. ACrO3 compounds crystallize in the orthorhombic GdFeO3type perovskite structure (space group Pnma).10,11,35−43 They are canted antiferromagnets with weak ferromagnetic moments. The Néel magnetic transition temperature (TN) decreases with decreasing radius of the A3+ ions (e.g, TN = 288 K in LaCrO3 and TN = 112 K in LuCrO3).35,41 Some ACrO3 compounds with A = Nd, Sm, Gd, and Er show Cr3+-spin-reorientation transitions at lower temperatures.38,39 At very low temperatures, spins of A3+ ions undergo antiferromagnetic (AFM) ordering.38,39 Some members of the ACrO3 family show magnetization reversal (or negative magnetization) phenomena.36 A new concept of local noncentrosymmetry was proposed to explain the observed “ferroelectric-like” anomalies near 400−500 K on the temperature dependence of the dielectric constant of ACrO3 (A = Ho−Lu and Y).10,11 However, straightforward confirmations of ferroelectricity of ACrO3 (A = Ho−Lu and Y) have not been demonstrated yet in contrast to the La1−xBixCrO3 system where ferroelectric hysteresis loops were observed.12 The formation of orthorhombic perovskite-type chromites with small A3+ cations (InCrO3 and ScCrO3) under high pressure was reported a long time ago as mentioned above.21,23 However, to the best of our knowledge, their properties have not been investigated yet. The crystal structure (atomic coordinates) was reported for ScCrO3.21 For InCrO3, the crystal system and lattice parameters were only determined.23 In this work, we report on the high-pressure synthesis, crystal structures, thermal properties, and physical properties of “exotic” perovskites InCrO3 and ScCrO3 studied with specific heat, dc and ac magnetization, and dielectric measurements. Physical properties of InCrO3 and ScCrO3 were compared with those of a “typical” perovskite YCrO3 with nonmagnetic Y3+ ions at the A site, and some features of InCrO3 and ScCrO3 in comparison with other members of the ACrO3 family were found.

density of the ScCrO3 (ρexp = 4.80(2) g/cm3) and InCrO3 (ρexp = 6.75(2) g/cm3) pellets exceeded 98% of the theoretical density. The density was measured using the Archimedes method using CCl4 with the density of 1.587 g/cm3. Single-phase YCrO3 was prepared at ambient pressure by annealing a pelletized stoichiometric mixture of Y2O3 (99.99%) and Cr2O3 (99.99%) at 1430 K for 75 h and 1670 K for 30 h on Pt plates with several intermediate grindings. The density of YCrO3 pellets prepared at ambient pressure (∼5.24(2) g/cm3) was below 90% of the theoretical density. Therefore, YCrO3 was then treated at 6 GPa and 1700 K for 40 min. This procedure resulted in pellets with the density of 5.73(2) g/cm3 (about 99.6% of the theoretical density). The highpressure YCrO3 sample was used in dielectric and specific heat measurements. X-ray powder diffraction (XRPD) data of ScCrO3 and InCrO3 collected at RT on a RIGAKU Ultima III diffractometer using Cu Kα radiation (2θ range of 19−150°, a step width of 0.02°, and a counting time of 30 s/step) showed that the samples contained a small amount of Cr2O3 as an impurity. Synchrotron XRPD data were measured at RT on a large Debye−Scherrer camera at the BL15XU beamline of SPring-8.44 The data were collected between 2° and 60° at the 0.003° interval in 2θ. The incident beam was monochromatized at λ = 0.63043 Å (ScCrO3) and 0.65297 Å (InCrO3). The samples were packed into Lindenmann glass capillaries (inner diameter: 0.1 mm), which were rotated during the measurement. The Rietveld analysis was performed with RIETAN-2000.45 For the impurity of Cr2O3, we refined only a scale factor and the lattice parameters, fixing its structure parameters. Magnetic susceptibilities (χ = M/H) of ScCrO3, InCrO3, and YCrO3 were measured using pellets on a SQUID magnetometer (Quantum Design, MPMS) between 2 and 400 K in different applied fields under both zero-field-cooled (ZFC) and field-cooled (FC, on cooling) conditions. Isothermal magnetization measurements were performed between −50 and 50 kOe (and between 0 and 70 kOe) at different temperatures. Specific heat, Cp, at magnetic fields of 0 and 70 kOe was recorded between 2 and 300 K on cooling by a pulse relaxation method using a commercial calorimeter (Quantum Design PPMS). Frequency dependent ac susceptibility measurements at a zero static magnetic field were performed with a Quantum Design MPMS instrument from 150 to 2 K at frequencies ( f) of 0.5, 1.99, 7, 25, 110, and 299.5 Hz and an applied oscillating magnetic field (Hac) of 5 Oe. We also measured the ac susceptibilities at zero static magnetic field and frequency of 110 Hz at different Hac (0.05, 0.5, and 5 Oe) from 150 to 2 K. No frequency or ac field dependence was observed. Dielectric properties were measured using an Agilent E4980A LCR meter between 5 and 300 K in the frequency range of 100 Hz and 2 MHz at magnetic fields of 0 and 90 kOe. Differential scanning calorimetry (DSC) curves of ScCrO3 and InCrO3 were recorded on a SII Exstar 6000 (DSC 6220) system at a heating/cooling rate of 10 K/min from 290 to 873 K (three runs) in

2. EXPERIMENTAL SECTION ScCrO3 and InCrO3 were prepared from stoichiometric mixtures of In2O3 (99.99%), Sc2O3 (99.9%), and Cr2O3 (99.99%). The mixtures were placed in Au capsules and treated at 6 GPa in a belt-type high pressure apparatus at 1500 K for 2 h (heating rate to the desired temperature was 10 min). After heat treatment, the samples were quenched to room temperature (RT), and the pressure was slowly released. The resultant samples were dark-green dense pellets. The 2198

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semiclosed aluminum capsules. The thermal stability of ScCrO3 and InCrO3 in air was also examined on a SII Exstar 6000 (TG-DTA 6200) system between 290 and 1340 K at a heating−cooling rate of 10 K/ min using Pt holders.

3. RESULTS AND DISCUSSION The structure parameters of ScCrO321 and YCrO311 were used as the initial ones for the refinements of ScCrO3 and InCrO3. The refined structural parameters, R values, selected bond lengths, and bond-valence sums46 are listed in Tables 1 and 2. Table 2. Selected Bond Lengths, l (Å), Bond Angles (deg), Bond Valence Sums, BVS, and Distortion Parameters of CrO6, Δ, in ScCrO3 and InCrO3a ScCrO3 Sc−O1 Sc−O2 (×2) Sc−O1 Sc−O2 (×2) Sc−O2 (×2) BVS(Sc3+) Cr−O2 (×2) Cr−O2 (×2) Cr−O1 (×2) BVS(Cr3+) Δ(Cr−O) Cr−O1−Cr Cr−O2−Cr

InCrO3 2.074(1) 2.101(1) 2.124(1) 2.379(1) 2.634(1) 2.75 1.962(1) 1.962(1) 1.991(1) 3.07 0.48 × 10−4 135.68(5) 138.96(5)

In−O1 In−O2 (×2) In−O1 In−O2 (×2) In−O2 (×2) BVS (In3+) Cr−O2 (×2) Cr−O2 (×2) Cr−O1 (×2) BVS(Cr3+) Δ(Cr−O) Cr−O1−Cr Cr−O2−Cr

2.121(2) 2.132(1) 2.168(2) 2.454(1) 2.704(1) 2.79 1.973(2) 1.977(2) 2.021(1) 2.93 1.21 × 10−4 137.87(5) 140.86(5)

Figure 1. Experimental, calculated, and difference synchrotron XRPD diffraction profiles for (a) InCrO3 and (b) ScCrO3. The bars show possible Bragg reflection positions for the Pnma phase and the Cr2O3 impurity (from top to bottom). The inset shows the enlarged fragment for InCrO3.

BVS = ∑Ni=1νi, νi = exp[(R0 − li)/B], N is the coordination number, B = 0.37, R0(In3+) = 1.902, R0(Sc3+) = 1.849, and R0(Cr3+) = 1.724.46 Δ = (1/N)∑Ni=1[(li − lav)/lav]2, where lav = (1/N)∑Ni=1li is the average Cr−O distance and N is the coordination number (N = 6). a

Experimental, calculated, and difference synchrotron XRPD profiles are shown in Figure 1. The structural parameters of ScCrO3 are very close to the previous results.21 Figure 2 depicts the crystal structure of ScCrO3. The Néel temperature of ScCrO3 and InCrO3 decreases with decreasing the radius of cations at the A site in agreement with the general tendency of the ACrO3 family (the inset of Figure 3). It can be attributed to the decrease of the Cr−O−Cr bond angles (Table 2; ∠(Cr−O1−Cr) = 159.07° and ∠(Cr−O2− Cr) = 161.33° in LaCrO347 and ∠(Cr−O1−Cr) = 144.33° and ∠(Cr−O2−Cr) = 147.67° in ErCrO3)38 and, as a result, to the decrease of the strength of the nearest neighbor AFM interactions between Cr3+ ions. The monotonic decrease of the corresponding bond angles was observed in other families, for example, in AMnO3 from about 155° in LaMnO3 to 140° in LuMnO348 to 135.0−143.4° in (In0.75Mn0.25)MnO3.17 However, magnetic properties of ScCrO3 and InCrO3 themselves are different from those of ACrO3 (A = La−Lu and Y). ScCrO3 and InCrO3 demonstrate extremely weak ferromagnetic properties. First, no detectable hysteresis loops were observed on the M vs H curves (Figure 4) compared with the well-defined hysteresis loops in YCrO3 where the coercive field exceeds 10 kOe and the remnant magnetization is about 0.03μB at 5 K (see the inset of Figure 4 and ref 40). Second, the FC susceptibility curves at small magnetic fields (e.g., 100 Oe) reach only 0.02 cm3 mol−1 (3.6 × 10−4 μB/fu) (Figure 3) compared with about 1.5 cm3 mol−1 (2.7 × 10−2 μB/fu) in YCrO3 (see Supporting Information and ref 40). Third, at large magnetic fields, the FC susceptibility curves of ScCrO3 and

Figure 2. Crystal Structure of ScCrO3.

InCrO3 just show a maximum at TN and a decrease below TN in comparison with a step-like increase in YCrO3 (Figure 5 and Supporting Information). The M vs H curves of ScCrO3 and InCrO3 at 5 K showed an up-turn deviation from the linear behavior at high magnetic fields (Figure 4). This indicates an increase of a ferromagnetic contribution and a possible field-induced phase transition above 70 kOe. A field-induced magnetic transition was observed in YCrO3.43 Despite the absence of hysteresis in ScCrO3 and InCrO3 the magnetization reaches about 0.05μB at 5 K and 50 kOe. This value is comparable with the magnetization of YCrO3, which reaches 0.075μB at 5 K and 50 kOe (Figure 4). The ac susceptibility data showed that there are actually two transitions with close temperatures. The first transition at 73 K in ScCrO3 may correspond to a pure AFM transition because 2199

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Figure 6. Real χ′ and imaginary χ″ parts of the ac susceptibility as a function of temperature (2−150 K) of ScCrO3 and InCrO3. Measurements were performed on cooling at zero static field using the ac field with the amplitude Hac = 5 Oe and frequency f = 110 Hz.

Figure 3. ZFC (filled symbols) and FC (measured on cooling; white symbols) dc magnetic susceptibility (χ = M/H) curves of ScCrO3 and InCrO3 at 100 Oe. The inset shows the dependence of the Néel temperature (TN)35,41 on the ionic radius of the A-type cations (in eightfold coordination) in ACrO3 (A = La−Lu and Y), InCrO3, and ScCrO3.

Figure 4. Isothermal magnetization curves of ScCrO3 and InCrO3 at 5 K. The insert shows the M vs H curves of YCrO3 at 5 K.

there were peaks on the real part of the ac susceptibilities (Figure 6) and no anomalies on the imaginary part of the ac susceptibilities (Figure 7). The second transition takes place at 68.6 K in ScCrO3, and it has very sharp peaks (the width of the peak was about 1 K on the χ″ vs T curves) on both χ′ vs T and

Figure 7. Real χ′ and imaginary χ″ parts of the ac susceptibilities of ScCrO3 and InCrO3 near TN.

χ″ vs T curves. The peak on the χ″ vs T curves indicates the appearance of a weak ferromagnetic moment. The similar features were observed in InCrO3 but with significantly decreased intensities for the second anomaly. In the case of YCrO3, only one rather broad anomaly (the width of the peak was about 9 K on the χ″ vs T curves) was found at TN on both χ′ vs T and χ″ vs T curves in agreement with the onset of the canted AFM ordering (see Supporting Information). The magnetic susceptibilities of ScCrO3 and InCrO3 were very close to each other above 150 K (Figure 3). The inverse FC magnetic susceptibilities (at 10 kOe) between 290 and 400 K were fit by the Curie−Weiss equation χ (T ) = μeff 2 N (3kB(T − θ ))−1

(1)

where μeff is effective magnetic moment, N is Avogadro’s number, kB is Boltzmann’s constant, and θ is the Weiss constant. The fitting parameters are μeff = 3.965(7)μB and θ = −187(2) K for ScCrO3, μeff = 3.945(11)μB and θ = −167(3) K for InCrO3, and μeff = 3.958(5)μB and θ = −318(2) K for

Figure 5. Inverse field-cooled FC dc magnetic susceptibility (χ−1 = H/ M) curves of ScCrO3 and InCrO3 at 10 kOe measured on cooling. The lines show the Curie−Weiss fits between 290 and 400 K with the fitting parameters given in the text. 2200

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YCrO3 (Figure 5). The effective magnetic moments of three samples were very close to each other and close to the localized Cr3+ moment of 3.87μB. Fitting in a different temperature range resulted in slightly different parameters (see Supporting Information). Specific heat of ScCrO3 and InCrO3 shows typical sharp anomalies near TN (Figure 8) indicating the onset of long-range

Figure 8. Specific heat data of ScCrO3 (circles) and InCrO3 (squares) at 0 and 70 kOe and YCrO3 at 0 Oe (crosses) plotted as Cp/T vs T. The thin line shows the lattice contribution to the specific heat of InCrO3 obtained from the experimental specific heat of InRhO3. The inset gives temperature dependence of the magnetic entropy in InCrO3.

Figure 9. Temperature dependence of (a) the dielectric constant and (b) loss tangent in ScCrO3 (the left-hand axes) and InCrO3 (the righthand axes) at different frequencies. The vertical arrows show the Néel temperatures (TN).

magnetic ordering. The magnetic field of 70 kOe just smeared a little bit the anomalies near TN without noticeable changes in the maximum positions indicating the robustness of the AFM state. The lattice contribution (CL) to the total specific heat (Cp) of InCrO3 was estimated using the experimental specific heat of isostructural nonmagnetic InRhO 3 (C L = 0.98Cp(InRhO3)).23 The magnetic specific heat (Cm) was obtained as Cm(InCrO3) = Cp(InCrO3) − CL. The magnetic entropy was obtained using the equation

Sm =

∫ (Cm/T ) dT

noticeably larger. Note that the loss tangent of ScCrO3 was significantly smaller (Figure 9b) than that of InCrO3 and YCrO3 in the whole temperature range of 5−300 K and even in the region of the dielectric relaxation. No anomalies were observed on the DSC curves of ScCrO3. The first heating DSC curve of InCrO3 showed a very broad anomaly between 570 and 740 K. However, no anomalies were found on the cooling curves and the second and third heating curves. Therefore, the origin of the first anomaly in InCrO3 is likely to be annealing effects sometimes observed in samples prepared at high pressure. The XRPD data collected after the DSC experiments showed no change in the phase composition (see Supporting Information). No anomalies were found on the differential thermal analysis (DTA) curves up to 1340 K. The XRPD data collected after the TG/DTA experiments showed no change in the phase composition of ScCrO3, but InCrO3 partially decomposed: it consisted of InCrO3 (∼60%), Cr2O3, the ambient-pressure cubic phase of In2O3, and the “highpressure” rhombohedral phase of In2O3. The absence of any anomalies on the DTA curves of InCrO3 indicates that the decomposition proceeds slowly. Therefore, both ScCrO3 and InCrO3 show remarkable thermal stability for the high-pressure phases. This fact suggests that the synthesis of ScCrO3 and InCrO3 could be achieved without the application of high pressure of 6 GPa through “low-temperature” synthetic methods (e.g., below 1273 K) such as the hydrothermal method,35 a citrate sol−gel route,52 or other methdods.53 We note that the high-pressure synthesis at 6 GPa has one big advantage of producing ceramics with almost 100% density. The canted antiferromagnetism of ACrO3 is attributed to the Dzyaloshinskii-Moriya interaction. The symmetry of ScCrO3,

(2) −1

−1

The Sm value was 9.04 K mol , which is smaller than the spin-only value of R ln(2S + 1) = R ln 4 = 11.53 J K−1 mol−1 expected for an S = 3/2 system (S is spin). The dielectric constant of ScCrO3 and InCrO3 shows a curvature at TN (Figure 9). This curvature is very similar to the anomalies observed in hexagonal InMnO3, LuMnO3, and YMnO3 at TN.49,50 The anomaly near TN gives evidence about the magnetoelectric coupling in ScCrO3 and InCrO3. It is interesting that no dielectric anomalies were observed in YCrO3 near TN (see Supporting Information). This is another difference between ScCrO3 (InCrO3) and the other members of the ACrO3 family. The magnetic field of 90 kOe had almost no effect on the dielectric constant of ScCrO3 and InCrO3 (see Supporting Information). Two dielectric relaxations were observed in ScCrO3 (at 30−40 K and 140−180 K) and InCrO3 (at 170−220 K and 270−300 K) (Figure 9). Their origin may come from different conductivity processes (for example, on electrode interfaces, grain boundaries, and in bulk). The relaxation behavior is often observed in perovskites due to electronic and ionic conductivities.51 The dielectric constant of ScCrO3 (ε ∼ 23−26) and YCrO3 (ε ∼ 18−19) at low temperatures was close to the reported values for ErCrO3 (ε ∼ 23).37 The dielectric constant of InCrO3 (ε ∼ 75−80) was 2201

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interest in these compounds from experimentalists and theoreticians.

InCrO3, and ACrO3 is the same. Therefore, the DzyaloshinskiiMoriya interaction is allowed in ScCrO3 and InCrO3, and they indeed show weak ferromagnetic properties. However, the weak ferromagnetic moment due to canting of antiferromagnetically ordered spins is extremely small in ScCrO3 and InCrO3. The apparent disappearance of canting caused by the Dzyaloshinskii-Moriya interaction could be attributed to the increased structural distortions in ScCrO3 and InCrO3 in comparison with YCrO3 and LuCrO3. The Néel temperature of ScCrO3 and InCrO3 decreases because the Cr−O−Cr nearest neighor (NN) superexchange interactions are weakened. On the other hand, the next nearest neighor (NNN) interactions (Cr−O− O−Cr) become stronger, and the competition between the NN and NNN interactions enhances. In the case of ScVO3, this competition gives a different magnetic structure in comparison with AVO3.18 In AMnO3 (A = La−Lu and Y), this competition produces incommensurate magnetic structures for A = Tb and Dy and multiferroic properties.8,48 Magnetic properties of ScCrO3 and InCrO3 also show some peculiarities, namely, the double-peak anomalies near TN (Figure 7), which have not been observed in ACrO3. ABO3 perovskites with A = La−Lu and Y and B = V, Cr, Mn (except for A = Ho−Lu and Y), and Fe can easily be prepared at ambient pressure. In the case of A = Sc and In, the stabilization of perovskite-type phases requires high-pressure high-temperature conditions. But even with the high-pressure high-temperature treatment some perovskite phases cannot be reached, for example, ScMnO3 and InMnO3 keep the ambientpressure hexagonal structure,49,54 ScFeO355 and InFeO356 are stabilized in corundum-type structures (in comparison with the ambient-pressure bixbyite32 and YAlO3-type structures,28 respectively), and our attempts to synthesize ScCoO 3, InCoO3, ScNiO3, and InNiO3 at high pressure of 6 GPa were unsuccessful. Therefore, the existence (and high thermal stability) of ScCrO3 and InCrO3 perovskites is unusual itself. We also investigated solid solutions InCr1−xMxO3 and ScCr1−xMxO3 (M = Mn and Fe). InCr0.5Fe0.5O3 contained about 20 wt % of impurities with the corundum structure, while InCr0.7Fe0.3O3 was single-phase with a = 5.3642(1) Å, b = 7.5865(1) Å, c = 5.1782(1) Å (see Supporting Information). Both InCr0.5Mn0.5O3 and InCr0.7Mn0.3O3 contained impurities with the corundum structure (and a very small amount of InOOH). ScCr0.5Fe0.5O3 was almost single-phase (with traces of Sc2O3 impurity) with a = 5.3734(1) Å, b = 7.4643(1) Å, c = 5.0523(1) Å in agreement with the results of ref 55. The parameters of the Curie−Weiss fit (between 300 and 750 K) were μeff = 5.128(3)μB and θ = −641(1) K for ScCr0.5Fe0.5O3 (see Supporting Information) indicating strong antiferromagnetic coupling between magnetic ions. ScCr 0.5 Mn 0.5 O 3 contained a significant amount of Sc2O3 impurity. Therefore, the composition of a perovskite phase could shift similar to (In1−xMnx)MnO3 with 0.111 ≤ x ≤ 0.333.17 Almost a singlephase sample with the total composition of Sc0.8Cr0.5Mn0.5O2.7 was indeed prepared, but it had significant anisotropic broadening of some reflections (see Supporting Information). In summary, we have investigated structural, magnetic, and dielectric properties of ScCrO3 and InCrO3. ScCrO3 and InCrO3 behave differently from other members of the ACrO3 family in some aspects, including the presence of dielectric anomalies at TN, extremely weak ferromagnetic properties, and the double-peak anomalies near TN. They also show remarkable thermal stability. We hope that our results will stimulate further

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ASSOCIATED CONTENT

* Supporting Information S

Full reference 55; detailed magnetic and dielectric properties of YCrO3; more details of magnetic and dielectric properties of ScCrO3 and InCrO3; XRPD patterns of ScCrO3 and InCrO3 before and after DSC and TG/DTA experiments; and XRDP patterns and magnetic data of InCr1−xMxO3 and ScCr1−xMxO3 (M = Mn and Fe) (PDF). This information is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by World Premier International Research Center Initiative (WPI Initiative, MEXT, Japan), the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program)”, and the Grants-inAid for Scientific Research (22246083) from JSPS, Japan. The synchrotron radiation experiments were performed at the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (Proposal Numbers: 2009B4505 and 2011B4512).

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