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1

Dynamic Disorder in Perovskites: Local Symmetry Breaking at the Sr Site in SrTiO_3

100%

Blinc R., Zalar B., Laguta V., Zidanšek A.

Acta Physica Polonica A

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2005

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vol. 108

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issue 1

7-11

EN

A-site symmetry breaking in the macroscopically cubic paraelectric phase of SrTiO_3 was observed by quadrupole perturbed ^{87}Sr NMR. The local symmetry breaking at the A (Sr) site is connected with slow and biased disorder dynamics similarly as at the B (Ti) site.

2

Details of Magnetic Properties in Pb(Fe_{1/2}Nb_{1/2})O_{3}

100%

Maryško M., Laguta V., Raevski I.

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vol. 126

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issue 1

376-377

EN

For Pb(Fe_{0.5}Nb_{0.5})O_{3} the χ(T) and m(H) measurements up to 70 kOe were performed with the aim to estimate the antiferromagnetic (AFM) and superantiferromagnetic (SAF) contribution to χ(T). Below T_{N} the increase of χ(T) is attributed to a small part of Fe^{3+} ions in the SAF clusters. For high fields the suppression of the AFM and enhancement of the SAF susceptibility was observed. An inflection point of the m(H) curves below the Néel point suggests the presence of a spin reorientation process connected with the AFM phase.

3

The Local Order in KTaO_3 Admixtured by the Ions of Li^+

88%

Kaszyńska K., Trybuła Z., Glinchuk M., Bykov I., Laguta V.

Acta Physica Polonica A

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2005

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vol. 108

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issue 2

379-383

EN

The low temperature behavior of the KTaO_3 type incipient ferroelectric crystals is of constant interest. The quantum fluctuations reduce the transition to the ferroelectric state in these crystals. It is possible that the small amount of the dopant Li^+ can lead, through the elastic interactions, to local glass-like short-range order or even to the relaxor ferroelectric order for x>2.6%. We presented that the low lithium doped x=0.005 KTaO_3 crystals exhibit the dielectric dispersion ofε andε", suggesting the glass-like behavior in the low temperature range.

4

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

76%

Glinchuk M., Kondakova I., Laguta V., Slipenyuk A., Bykov I., Ragulya A., Klimenko V.

Acta Physica Polonica A

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2005

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vol. 108

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issue 1

47-60

EN

The theoretical and experimental investigation of ferroelectric nanopowders is performed. The manifestation in radiospectroscopy spectra of size driven ferroelectric-paraelectric phase transition at some critical particle average size R = R_c was the main goal of the consideration. In theoretical part the size effect for the materials with ferroelectric tetragonal phase at room temperature and cubic paraelectric phase was considered allowing for the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes. In ESR the transformation of the spectra from tetragonal symmetry to cubic symmetry lines with decrease in nanoparticle sizes was calculated. The method of R_c value extraction from the ratio of the different symmetry lines intensities in the absorption spectra was proposed. Measurements of Fe^{3+} ESR spectra in nanopowder of BaTiO_3 were carried out at room temperature. The samples were prepared by rate-controlled method with different particle sizes, which depend on annealing temperature. The decrease in intensity of tetragonal symmetry ESR lines of Fe^{3+} and appearance of cubic symmetry line with asymmetry of the shoulders was observed with the average sizes decrease with complete disappearance of tetragonal spectrum at R ≤ 40 nm. The comparison of the theory with experiment was carried out. The theory fits experimental data pretty good. The value of critical size R_c ≈ 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface with lower than cubic symmetry. The deconvolution of the cubic line allowed to show that this region size is about 3 nm.

5

NMR Study of Multiferroic Iron Niobate Perovskites

76%

Kouřil K., Chlan V., Štěpánková H., Řezníček R., Laguta V., Raevski I.

Acta Physica Polonica A

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2015

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vol. 127

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issue 2

234-236

EN

We present ^{93}Nb, ^{207}Pb and ^{135,137}Ba NMR study of multiferroic lead iron niobate and barium iron niobate ceramics. We ascribe development of NMR spectra on cooling below room temperature to magnetism of ferric ions close to resonating nuclei and introduce a framework capable of describing key features of the observed temperature induced changes. We show that the ferric ions have much stronger influence on hyperfine fields at nuclei of large cations in lead compound and estimate strength of interaction of superantiferromagnetic clusters.

6

Cluster Superconductivity in the Magnetoelectric Pb(Fe_{1/2}Sb_{1/2})O₃ Ceramics

52%

Laguta V., Marysko M., Stephanovich V., Raevsky I., Olekhnovich N., Pushkarev A., Radyush Y., Raevskaya S., Kuzian R., Chlan V., Štěpánková H.

Acta Physica Polonica A

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2017

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vol. 131

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issue 6

1534-1539

EN

We report the observation of cluster (local) superconductivity in the magnetoelectric Pb(Fe_{1/2}Sb_{1/2})O₃ ceramics prepared at a hydrostatic pressure of 6 GPa and temperatures 1200-1800 K to stabilize the perovskite phase. The superconductivity is manifested by an abrupt drop of the magnetic susceptibility at the critical temperature T_{c} ≈7 K. Both the magnitude of this drop and T_{c} decrease with magnetic field increase. Similarly, the low-field paramagnetic absorption measured by EPR spectrometer drops significantly below T_{c} as well. The observed effects and their critical magnetic field dependence are interpreted as manifestation of the superconductivity and the Meissner effect in metallic Pb nanoclusters existing in the ceramics. Their volume fraction and average size were estimated as 0.1-0.2% and 140-150 nm, respectively. The superconductivity related effects disappear after oxidizing annealing of the ceramics.

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6 Acta Physica Polonica A

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6 Laguta V.

2 Bykov I.

2 Chlan V.

2 Glinchuk M.

2 Raevski I.

2 Štěpánková H.

1 Blinc R.

1 Kaszyńska K.

1 Klimenko V.

1 Kondakova I.

1 Kouřil K.

1 Kuzian R.

1 Marysko M.

1 Maryško M.

1 Olekhnovich N.

1 Pushkarev A.

1 Radyush Y.

1 Raevskaya S.

1 Raevsky I.

1 Ragulya A.

1 Slipenyuk A.

1 Stephanovich V.

1 Trybuła Z.

1 Zalar B.

1 Zidanšek A.

1 Řezníček R.

Dynamic Disorder in Perovskites: Local Symmetry Breaking at the Sr Site in SrTiO_3

Details of Magnetic Properties in Pb(Fe_{1/2}Nb_{1/2})O_{3}

The Local Order in KTaO_3 Admixtured by the Ions of Li^+

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

NMR Study of Multiferroic Iron Niobate Perovskites

Cluster Superconductivity in the Magnetoelectric Pb(Fe_{1/2}Sb_{1/2})O₃ Ceramics