Abstract:High‐pressure neutron diffraction measurements of polycrystalline LaFeO3 are collected up to 5.5 and 6.4 GPa at 290 and 110 K, respectively. The bulk moduli are determined as B0(290 K) = 170(3) GPa and B0(110 K) = 175(1) GPa. The unit cell is found to compress anisotropically at both temperatures with the a‐axis compressing preferentially. A crossover in lattice parameters is observed, from a > c to c > a, at 2 GPa at 290 K and at 1.7 GPa at 110 K. The magnetic moment remains unchanged over the pressure range … Show more
“…By contrast, B-site cation size has the opposite influence on the tilts in the series LaBO 3 (B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). There is an approximately linear decrease in the tilts with reduction in B-site cation radius from Sc to Fe [25,[53][54][55][56][57], and an eventual raising of symmetry to rhombohedral for the Co-Cu compounds.…”
Section: Resultsmentioning
confidence: 94%
“…By contrast, B-site cation size has the opposite influence on the tilts in the series LaBO3 (B=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). There is an approximately linear decrease in the tilts with reduction in B-site cation radius from Sc to Fe [25,53–57], and an eventual raising of symmetry to rhombohedral for the Co-Cu compounds. Figure 3Calculated anti-phase, a− ( a ), and in-phase, c+ ( b ), tilt angles plotted as a function of A-site ionic radius for a number of lanthanide orthochromites found in the literature [22,27–50], and from the present study.…”
Section: Resultsmentioning
confidence: 99%
“…On continued heating, the tetragonal strain remains unchanged, while the modulus of the shear strain begins to increase again. This phenomenon is not unusual in orthorhombic perovskites; while the crossover is usually induced through changes in chemical composition, it is well documented as a temperature effect in [ 24 , 25 ]. The origins of this crossover are the competition between the octahedral tilting, and octahedral distortion.…”
The nuclear and magnetic structure of
PrCrO
3
has been investigated using neutron and X-ray powder diffraction as a function of pressure and temperature. The orthorhombic symmetry (space group
P
b
n
m
) remains stable up to the highest temperature (1500 K) and pressure (approx.
6
GPa
) considered. There is a crossover in the magnitude of the
a-
and
b
-lattice parameters at approximately 1135 K, caused by competing effects of octahedral tilting and distortion. The material is antiferromagnetic (
T
N
≈
240
K) with
P
b
′
n
′
m
symmetry, with a maximum moment of
2.34
(
2
)
μ
b
on the
Cr
3
+
sites aligned along the direction of the
a
-axis. The application of pressure shows an abnormal softening in the unit-cell volume, which is suggestive of a continuous approach to a second-order phase transition. Raman spectroscopy measurements at ambient temperature were collected as a function of pressure up to approximately
12
GPa, with discontinuous mode behaviour further suggesting the existence of a transition above 7 GPa. The measured structural changes in
PrCrO
3
are compared extensively in the wider context of other lanthanide orthochromites, and the comparative effects of
A
- and
B
-site substitution on the polyhedral tilts and distortion are discussed.
This article is part of the theme issue ‘Exploring the length scales, timescales and chemistry of challenging materials (Part 1)’.
“…By contrast, B-site cation size has the opposite influence on the tilts in the series LaBO 3 (B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). There is an approximately linear decrease in the tilts with reduction in B-site cation radius from Sc to Fe [25,[53][54][55][56][57], and an eventual raising of symmetry to rhombohedral for the Co-Cu compounds.…”
Section: Resultsmentioning
confidence: 94%
“…By contrast, B-site cation size has the opposite influence on the tilts in the series LaBO3 (B=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu). There is an approximately linear decrease in the tilts with reduction in B-site cation radius from Sc to Fe [25,53–57], and an eventual raising of symmetry to rhombohedral for the Co-Cu compounds. Figure 3Calculated anti-phase, a− ( a ), and in-phase, c+ ( b ), tilt angles plotted as a function of A-site ionic radius for a number of lanthanide orthochromites found in the literature [22,27–50], and from the present study.…”
Section: Resultsmentioning
confidence: 99%
“…On continued heating, the tetragonal strain remains unchanged, while the modulus of the shear strain begins to increase again. This phenomenon is not unusual in orthorhombic perovskites; while the crossover is usually induced through changes in chemical composition, it is well documented as a temperature effect in [ 24 , 25 ]. The origins of this crossover are the competition between the octahedral tilting, and octahedral distortion.…”
The nuclear and magnetic structure of
PrCrO
3
has been investigated using neutron and X-ray powder diffraction as a function of pressure and temperature. The orthorhombic symmetry (space group
P
b
n
m
) remains stable up to the highest temperature (1500 K) and pressure (approx.
6
GPa
) considered. There is a crossover in the magnitude of the
a-
and
b
-lattice parameters at approximately 1135 K, caused by competing effects of octahedral tilting and distortion. The material is antiferromagnetic (
T
N
≈
240
K) with
P
b
′
n
′
m
symmetry, with a maximum moment of
2.34
(
2
)
μ
b
on the
Cr
3
+
sites aligned along the direction of the
a
-axis. The application of pressure shows an abnormal softening in the unit-cell volume, which is suggestive of a continuous approach to a second-order phase transition. Raman spectroscopy measurements at ambient temperature were collected as a function of pressure up to approximately
12
GPa, with discontinuous mode behaviour further suggesting the existence of a transition above 7 GPa. The measured structural changes in
PrCrO
3
are compared extensively in the wider context of other lanthanide orthochromites, and the comparative effects of
A
- and
B
-site substitution on the polyhedral tilts and distortion are discussed.
This article is part of the theme issue ‘Exploring the length scales, timescales and chemistry of challenging materials (Part 1)’.
“…The small variation of H hf with temperature is the combined effect of the temperature change of the Fe magnetic moment and crystallographic unit cell parameters. For BiFeO 3 the Fe magnetic moment changes from 4.0 μ B at 300 K to 4.35 μ B at 77 K [21] and for LaFeO 3 the Fe magentic moment changes by approximately 0.5 μ B with the change of temperature from 290 K to 110 K [28]). At the same time, the change of the Fe -O -Bi/La angle is smaller than 0.1 • .…”
Hyperfine interactions in the Bi 1−x La x FeO 3 ferrites (where x = 0.0225, 0.075, 0.9) have been studied by means of 57 Fe Mössbauer spectroscopy and 140 Ce time differential perturbed angular γ -γ correlation methods. The information about the line shift δ, the lattice ε lat and the magnetic ε mag contributions to the quadrupole shift ε, isotropic H is and anisotropic H an contributions to the hyperfine magnetic field H hf on 57 Fe nuclei, anharmonicity parameter m, distribution of the hyperfine magnetic field p(H hf ), and supertransferred hyperfine magnetic fields on 140 Ce probe nuclei were obtained. In all studied compounds, the Fe ions are in a high-spin trivalent state. In the compounds with x = 0.0225 and 0.075 spatially modulated cycloidal magnetic structures exist. It was found that the sign of the effective constant of magnetic anisotropy K eff changes with the variation of x from 0.0225 to 0.075. The substitution of Bi by La increases the value of the hyperfine magnetic field on 57 Fe nuclei from 494 kOe in Bi 0.9775 La 0.0225 FeO 3 to 520 kOe in Bi 0.1 La 0.9 FeO 3 , i.e. by 26 kOe, while the corresponding supertransferred hyperfine magnetic field on 140 Ce probe nuclei decreases.
Keywords Hyperfine interactions • Mössbauer spectroscopy • TDPAC • MultiferroicsThis article is part of the Topical Collection on
“…Orthorhombic distortion for the LaFeO 3 structure of thin films obtained by PLD at different temperatures (dots). Values obtained from literature (squares) were reported for comparison[20,24,[29][30][31][32][33]. The line corresponds to a tetragonal distortion (x = y).…”
The orthorhombic LaFeO3 thin films grown by pulsed laser deposition on silicon showed nano-structuration of their surface and preferential crystallographic exposed facets, depending on the deposition temperature. The LaFeO3 film deposited at 850°C has two types of grain termination, flat or tip-like, corresponding to two different growth directions, respectively [110] and [200]. Due to the shape of the termination, the same {110} facets are exposed. The LaFeO3 is iron deficient and consequently contains oxygen vacancies, the exact chemical formula being LaFe0.82O3-delta.
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