Hyperfine interaction measurements in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">LaCrO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">LaFeO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>perovskites

Dogra, R.; Junqueira, A. C.; Saxena, R. N.; Carbonari, A. W.; Mestnik-Filho, J.; Moralles, M.

doi:10.1103/physrevb.63.224104

Cited by 98 publications

(94 citation statements)

References 21 publications

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“…In this approximation the only effect of the probe is to antishield the lattice contribution through the Sternheimer antishielding factor 12 , that for Cd is usually taken as: γ ∞ = −29.27 13 . PCM has been extensively used to predict EFG at Cd sites in perovskites and oxides 14,15,16,17 but calculations at the ab-initio level are rare in these systems because Cd usually enters the solid as impurity and this introduces several complications, as the effect of atomic relaxations, for example 18 . In the case of CdTiO 3 perovskite, Cd is one of the constituents of the system, so, accurate ab-initio calculations can be performed and used to check the validity of PCM aproximation.…”

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First-principles study of the orthorhombicCdTiO3perovskite

Fabricius

García

2002

Phys. Rev. B

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In this work we perform an ab-initio study of CdTiO3 perovskite in its orthorhombic phase using FLAPW method. Our calculations help to decide between the different cristallographic structures proposed for this perovskite from X-Ray measurements. We compute the electric field gradient tensor (EFG) at Cd site and obtain excellent agreement with available experimental information from a perturbed angular correlation (PAC) experiment. We study EFG under an isotropic change of volume and show that in this case the widely used "point charge model approximation" to determine EFG works quite well.PACS numbers: 77.84. Dy, 71.15.Nc Perovskites materials of the form ABO 3 have been intensively studied last years. In addition to the interest that present the technological aplications of ferroelectric materials, perovskites are known to undergo several phase transitions as a function of temperature that make them appealing for theoreticians and experimentalists. The transitions between different structures usually involve very little atomic displacements and are difficult to characterize, requiring some times several experimental techniques. First principles calculations have been playing an increasing role in the understanding of the these systems 1 . These studies not only try to give theoretical explanations to the observed phenomena, but usually give valuable information that help in the interpretation of the experimental results.CdTiO 3 perovskite has been the object of several studies using X-Ray diffraction 2,3,4 , dielectric properties methods 4,5,6 , infrared spectroscopy 7 and PAC technique 8,9 and there have been some difficulties and controversies in determining the symmetry group of it's orthorhombic structure at room temperature. In 1957 H.F.Kay and J.L.Miles established through XRay measurements that CdTiO 3 perovskite should have orthorhombic symmetry and non-centrosymmetric P bn2 1 10 space group with a large displacement of Ti atoms along the b axis 3 . However, the measurement of the electrical properties of CdTiO 3 single crystals couldn't resolve whether they were ferroelectric or not, then, the displacement of Ti atoms from their symmetric positions couldn't be confirmed 6 . In Reference 8 Baumvol and coworkers study the EFG at Cd in CdTiO 3 through PAC measurements. Using the Point Charge Model approximation (PCM) to estimate theoretically the EFG they infer that the structure of the perovskite couldn't be the one corresponding to P bn2 1 space group but should be another one with centrosymmetric space group, also considered and discarded by Kay&Miles. 4 performed new XRay studies on CdTiO 3 . They obtained that two orthorhombic structures with very similar coordinates and different space groups (centrosymmetric P bnm and noncentrosymmetric P bn2 1 ) fitted equally well the X-ray data. Analizing some structural and physical properties, they finally argued that it was more suitable to assign the space group P bnm to CdTiO 3 .The main objective of the present work is to clarify this picture, studying ...

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First-principles study of the orthorhombicCdTiO3perovskite

Fabricius

García

2002

Phys. Rev. B

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“…This is a typical feature of perovskite and related systems. 21 Below T c Ϸ 145 K both d and u local environments experience increasing magnetic hyperfine fields upon decreasing temperature ͑inset of Fig. 2͒, presenting at 10 K values of B hf d = 3.8͑2͒T and B hf u = 4.0͑3͒T compatible with a full ferromagnetic environment of the surrounding Mn ions.…”

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Percolative transition on ferromagnetic insulator manganites: Uncorrelated to correlated polaron clusters

et al. 2006

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We report an atomic-scale study on the ferromagnetic insulator manganite LaMnO 3.12 using ␥-␥ perturbed angular correlation spectroscopy. Data analysis reveals a nanoscopic transition from an undistorted to a JahnTeller ͑JT͒ distorted local environment upon cooling. The percolation thresholds of the two local environments enclose a macroscopic structural transition ͑rhombohedral-orthorhombic͒. Two distinct regimes of JT distortions were found: a high-temperature regime where uncorrelated polaron clusters with severe distortions of the Mn 3+ O 6 octahedra survive up to T Ϸ 800 K and a low-temperature regime where correlated regions have a weaker JT-distorted symmetry. DOI: 10.1103/PhysRevB.73.100408 PACS number͑s͒: 75.47.Lx, 31.30.Gs, 64.60.Ak, 76.80.ϩy Intense experimental and theoretical work has been devoted to manganite systems due to their colossal magnetoresistance ͑CMR͒, polaron dynamics, and charge-orbital ordering phenomena. The undoped manganites ͑AMnO 3 where A is a trivalent ion of La, Pr, . . .͒ typically show antiferromagnetic insulator behavior and cooperative Jahn-Teller ͑JT͒ distortion of MnO 6 octahedra. Oxygen excess or the presence of divalent ions at A sites reduce the static JT distortion by the creation of Mn 4+ ions. This effect favors the ferromagnetic interaction via dynamic electron transfer between Mn 3+ and Mn 4+ , the so-called double-exchange ͑DE͒ interaction. 1 Although DE interaction explains qualitatively the CMR, it does not fully account for the large resistivity of the paramagnetic and ferromagnetic insulator phases. Polaron formation must certainly play an important role in this respect. [2][3][4][5] Polarons are formed due to the strong electron-lattice coupling that leads to charge localization via JT distortions. Recently, the nature of such local distortions, their dynamics and correlations have been addressed by several authors. [6][7][8][9][10][11] In spite of such an effort, several issues as the detailed structure of polarons, the temperature evolution of polaron clusters, or the effect of such evolution on the average macroscopic lattice structure still remain as open questions.Local distortions and their dynamics can be studied by using ␥-␥ perturbed angular correlation spectroscopy ͑PAC͒, a nuclear hyperfine method specially effective to sample atomic-scale environments. PAC efficiency is T independent, allowing us to explore a wide range of temperatures. To gain further insight on the microscopic nature of polaronic distortions, their spatial correlations, and the role of polarons in ferromagnetic insulator manganites ͑FMI͒, we have studied in detail the compound LaMnO 3.12 using the PAC technique. This compound is a prototypical FMI manganite that undergoes a rhombohedral ͑R͒-orthorhombic ͑O͒ structural transition around room temperature, which provides us with an ideal scenario to probe the evolution of local lattice distortions through different average lattice symmetries. In particular, we show that random distributed polaron clusters survive in the undist...

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“…Thermal treatment of the sample, so that the probe atoms are introduced via diffusion or melting 33 2. Through chemical reaction, i.e., in situ preparation of sample with radioisotope probe 34 3. Implantation and/or recoil implantation of radioactive ions into the sample 35 Thermal treatment of the samples leads to a welldefined metallurgical state of the impurity in the respective semiconductor and is not suitable for semiconductors having low vapor pressure, e.g., Se, Te, and their compounds.…”

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The Potential of the Perturbed Angular Correlation Technique in Characterizing Semiconductors

Dogra¹,

Byrne

Ridgway

2009

Journal of Elec Materi

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Several experimental techniques are available to investigate materials but microscopic techniques based on hyperfine interaction form a subclass that can characterize materials at the smallest possible atomic scale. The interaction of the nuclear electromagnetic moments with the hyperfine fields arising from the extranuclear electronic charges and spin distributions forms the basis of hyperfine methods. In this review article, one of the hyperfine methods, known as perturbed angular correlation (PAC), has been described as it provides local-scale fingerprints about the formation, identification, and lattice environment of defects and/or defect complexes in semiconductors at the PAC probe site. In particular, the potential of the PAC technique has been demonstrated in terms of measured electric field gradient, its orientation, and the symmetry at the probe site for a variety of defects in semiconductors such as Si, InP, GaAs, InAs, ZnO, GaP, and InN.

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Hyperfine interaction measurements inLaCrO3andLaFeO3perovskites

Cited by 98 publications

References 21 publications

First-principles study of the orthorhombicCdTiO3perovskite

First-principles study of the orthorhombicCdTiO3perovskite

Percolative transition on ferromagnetic insulator manganites: Uncorrelated to correlated polaron clusters

The Potential of the Perturbed Angular Correlation Technique in Characterizing Semiconductors

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