[PDF] https://doi.org/10.3952/physics.v59i2.4012

Open access article / Atviros prieigos straipsnis
Lith. J. Phys. 59, 94–103 (2019)
 

PECULIARITIES OF CHARGE CARRIER RELAXATION IN GRAIN BOUNDARY OF GADOLINIUM-DOPED CERIA CERAMICS
  Saulius Kazlauskasa, Edvardas Kazakevičiusa, Artūras Žalgab, Saulius Daugėlaa, and Algimantas Kežionisa
 aInstitute of Applied Electrodynamics and Telecommunications, Saulėtekio 3, 10222 Vilnius, Lithuania
bDepartment of Applied Chemistry, Faculty of Chemistry and Geosciences, Vilnius University, Naugarduko 24,  03225 Vilnius, Lithuania
Email: saulius.kazlauskas@ff.vu.lt

Received 25 February 2019; revised 28 March 2019; accepted 2 April 2019

Two different gadolinium-doped ceria ceramics are prepared from two different powders, one commercially available synthesised by solid state reaction and another produced by tartaric acid assisted sol–gel synthesis. The specimens have a different microstructure, while the XRD patterns of powders showed a pure cubic fluorite structure without any impurity phase. The electrical properties are studied at frequencies up to 10 GHz by combining broadband 2-electrode and 4-electrode impedance spectroscopy methods. Primary electrical measurements showed that the values of grain conductivity and its activation energies for both ceramics were nearly the same. However, due to different contributions of the grain boundary mediums, total conductivities and their activation energies are found to be considerably different. The advantage of the 4-electrode method allowed us to measure the pure electrical response of grain boundaries, bypassing any interferences caused by interfacial impedance. By using these data, the temperature behaviour of distribution of relaxation times in the grain boundary is studied. A broadening of this distribution with increasing temperature is found for both specimens, contrary to a previously observed phenomenon in the grain of oxygen ion conductive ceramics and single crystals. It is shown that, supposing individual relaxation times behave according to the Arrhenius law, both activation energy and pre-exponential factor must be distributed.
Keywords: gadolinium-doped ceria, ionic conductivity, distribution of relaxation times, grain boundary, sintering
PACS: 81.05.Je, 66.30.Dn

KRŪVININKŲ RELAKSACIJOS YPATYBĖS TARPKRISTALITINĖJE GADOLINIU LEGIRUOTŲ CERIO OKSIDO KERAMIKŲ TERPĖJE
Saulius Kazlauskasa, Edvardas Kazakevičiusa, Artūras Žalgab, Saulius Daugėlaa, Algimantas Kežionisa

aVilniaus universiteto Taikomosios elektrodinamikos ir telekomunikacijų institutas, Vilnius, Lietuva
bVilniaus universiteto Chemijos ir geologijos fakultetas, Vilnius, Lietuva
 
Dviejų rūšių gadoliniu legiruoto cerio oksido keramikos buvo pagamintos iš skirtingų miltelių: vieni iš jų komerciniai, o kiti buvo sintezuojami zolių-gelių metodu, naudojant tartarinę rūgštį. Sukepintos keramikos turėjo skirtingą mikrostruktūrą, tačiau tyrimai rentgeno spindulių difrakcijos metodu rodė kubinio fluorito struktūrą be jokių priemaišinių fazių. Šių medžiagų elektrinės savybės buvo tiriamos iki 10 GHz dažniuose naudojant 2-jų ir 4-ių elektrodų pilnutinės varžos spektroskopijos metodus.
Pirminiai elektrinių savybių tyrimo rezultatai parodė, kad keramikų kristalitų laidumai ir jų aktyvacijos energijos yra identiški. Tačiau dėl skirtingų tarpkristalitinių terpių savybių bendrieji laidumai ir jų aktyvacijos energijos skyrėsi. Keturių elektrodų pilnutinės varžos spektroskopijos metodu buvo išmatuoti keramikų tarpkristalitinių terpių elektriniai atsakai. Pasitelkus šiuos duomenis buvo tiriamos krūvininkų relaksacijos trukmių pasiskirstymo keramikų tarpkristalitinėse terpėse temperatūrinės priklausomybės. Nustatyta, kad kylant temperatūrai šis pasiskirstymas didėja, priešingai, nei anksčiau stebėtame analogiškame reiškinyje joninio laidumo keramikų kristalituose ir monokristaluose. Taip pat parodyta, kad manant, jog atskiros relaksacijų trukmės kinta pagal Arenijaus dėsnį, tiek aktyvacijos energija, tiek priešeksponentinis faktorius turi būti pasiskirstę.

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