Publication detail

Grain Boundary and Size Effect on the Dielectric, Infrared and Raman Response of SrTiO3 Nanograin Ceramics

PETZELT, J. OSTAPCHUK, T. GREGORA, I. NUZHNYY, D. RYCHETSKÝ, I. MACA, K. SHEN, Z.

Original Title

Grain Boundary and Size Effect on the Dielectric, Infrared and Raman Response of SrTiO3 Nanograin Ceramics

English Title

Grain Boundary and Size Effect on the Dielectric, Infrared and Raman Response of SrTiO3 Nanograin Ceramics

Type

journal article - other

Language

en

Original Abstract

The recently revealed giant grain size effect on dielectric properties in undoped SrTiO3 ceramics (J. Petzelt et al., J. Phys.: Condens. Matter 19, 196222 (2007) and references therein), was extended to smaller grains of 80 nm mean grain size. Like for previously studied ceramics with larger grain size, in addition to dielectric permittivity also the infrared and Raman responses were studied and discussed. It was shown that the reduced effective permittivity is fully accounted for by the infrared soft mode behaviour and, similar to single crystals and other ceramics studied, no dielectric dispersion appears below the THz frequency range. The rather universal (independent of the grain size and sintering process) double dead layer structure was proposed to be responsible for the observed changes in the infrared and Raman spectra, allowing the grain core to keep the single crystal dielectric function. The outer dead layer shell (obviously charged due to an oxygen deficit) is very thin (ca 1 nm) having frequency and temperature independent low permittivity (ca 10) and is responsible for the static permittivity suppression. The inner layer of only slightly distorted perovskite structure is polar with local polarization normal to grain boundaries gradually decreasing towards the grain centre. This polarization and/or the thickness of the polar layers, which compensate the charged grain boundaries, appear to increase on decreasing temperature, particularly below the structural phase transition. Its nature is still not fully understood. In agreement with our previous suggestions, from the Raman data it can be also concluded that in the low-temperature tetragonal phase of all SrTiO3 ceramics, the local tetragonal axes tend perpendicular to the grain boundaries and the tetragonality is strongly reduced compared to single crystals.

English abstract

The recently revealed giant grain size effect on dielectric properties in undoped SrTiO3 ceramics (J. Petzelt et al., J. Phys.: Condens. Matter 19, 196222 (2007) and references therein), was extended to smaller grains of 80 nm mean grain size. Like for previously studied ceramics with larger grain size, in addition to dielectric permittivity also the infrared and Raman responses were studied and discussed. It was shown that the reduced effective permittivity is fully accounted for by the infrared soft mode behaviour and, similar to single crystals and other ceramics studied, no dielectric dispersion appears below the THz frequency range. The rather universal (independent of the grain size and sintering process) double dead layer structure was proposed to be responsible for the observed changes in the infrared and Raman spectra, allowing the grain core to keep the single crystal dielectric function. The outer dead layer shell (obviously charged due to an oxygen deficit) is very thin (ca 1 nm) having frequency and temperature independent low permittivity (ca 10) and is responsible for the static permittivity suppression. The inner layer of only slightly distorted perovskite structure is polar with local polarization normal to grain boundaries gradually decreasing towards the grain centre. This polarization and/or the thickness of the polar layers, which compensate the charged grain boundaries, appear to increase on decreasing temperature, particularly below the structural phase transition. Its nature is still not fully understood. In agreement with our previous suggestions, from the Raman data it can be also concluded that in the low-temperature tetragonal phase of all SrTiO3 ceramics, the local tetragonal axes tend perpendicular to the grain boundaries and the tetragonality is strongly reduced compared to single crystals.

Keywords

Strontium titanate nanoceramics; core-shell composite; dead layer; effective dielectric and infrared response; raman response

RIV year

2008

Released

01.01.2008

ISBN

0015-0193

Periodical

FERROELECTRICS

Year of study

363

Number

1

State

GB

Pages from

227

Pages to

244

Pages count

18

Documents

BibTex


@article{BUT49014,
  author="Jan {Petzelt} and Tetyana {Ostapchuk} and Ivan {Gregora} and Dimitry {Nuzhnyy} and Ivan {Rychetský} and Karel {Maca} and Zhijian {Shen}",
  title="Grain Boundary and Size Effect on the Dielectric, Infrared and Raman Response of SrTiO3 Nanograin Ceramics",
  annote="The recently revealed giant grain size effect on dielectric properties in undoped SrTiO3
ceramics (J. Petzelt et al., J. Phys.: Condens. Matter 19, 196222 (2007) and references
therein), was extended to smaller grains of 80 nm mean grain size. Like for previously
studied ceramics with larger grain size, in addition to dielectric permittivity also the infrared
and Raman responses were studied and discussed. It was shown that the reduced
effective permittivity is fully accounted for by the infrared soft mode behaviour and,
similar to single crystals and other ceramics studied, no dielectric dispersion appears
below the THz frequency range. The rather universal (independent of the grain size and
sintering process) double dead layer structure was proposed to be responsible for the
observed changes in the infrared and Raman spectra, allowing the grain core to keep the
single crystal dielectric function. The outer dead layer shell (obviously charged due to
an oxygen deficit) is very thin (ca 1 nm) having frequency and temperature independent
low permittivity (ca 10) and is responsible for the static permittivity suppression. The
inner layer of only slightly distorted perovskite structure is polar with local polarization
normal to grain boundaries gradually decreasing towards the grain centre. This
polarization and/or the thickness of the polar layers, which compensate the charged
grain boundaries, appear to increase on decreasing temperature, particularly below
the structural phase transition. Its nature is still not fully understood. In agreement
with our previous suggestions, from the Raman data it can be also concluded that in
the low-temperature tetragonal phase of all SrTiO3 ceramics, the local tetragonal axes
tend perpendicular to the grain boundaries and the tetragonality is strongly reduced
compared to single crystals.",
  chapter="49014",
  journal="FERROELECTRICS",
  number="1",
  volume="363",
  year="2008",
  month="january",
  pages="227--244",
  type="journal article - other"
}