Influence of temperature on AC conductivity of nanocrystalline CuAlO2

2016

J. Phys. Chem. C

Magnesium zirconium phosphate, MgZr4P6O24 (MZP) is a magnesium ion conducting ceramic material with potential for application as solid electrolyte in high temperature electrochemical sensor in non-ferrous scrap metal refining and virgin metal alloying operations. In this work, MZP was synthesised using a simple but novel and economical solgel route at a significantly reduced temperature. An insight into the calcination process, and possible phase transformation at higher temperature was obtained using simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Phase identification of the synthesised material was studied after calcining the powder at 900 o C for 3h using X-ray diffraction (XRD); a single monoclinic phase was observed at that temperature. However, a trace amount of possible minor second phase; zirconium oxide phosphate [Zr2(PO4)2O] was formed a T 1000 o C. Impedance spectroscopy measurement on platinised sintered-MZP pellets were carried out in the frequency range 100 mHz 32 MHz and in a temperature range of 30 -800 o C to determine the electrical properties of MZP. Ionic conductivity of MZP was found to be equal to 7.23x10 -3 -1 cm -1 at relatively lower, 725 o C. Furthermore, the Nyquist and modulus plots measured at 764 o C and 390 o C shows single semi-circles suggesting contribution from only grain interiors (GIs). The ionhopping rate was calculated by fitting the conductance spectra to the power law variation, ac dc A n . The ac and dc conductivity of MZP show Arrhenius-type of behaviour with activation energie Ea V SEM f the fractured MZP pellet sintered at 1300 o C for 24h revealed a highly dense microstructure with clearly visible grain boundaries and low porosity which is in good agreement with the relative density of ~99% determined A structure. EDS confirms the presence of Mg, Zr, P, O in appropriate atomic ratio to yield MgZr4P6O24. Finally, TEM on MZP particles with crystallite size of ~50nm also confirmed MZP as stable at 900 o C with no observable second phase, Zr2(PO4)2O.

Section: Resultssupporting

confidence: 70%

Novel Sol–Gel Synthesis of MgZr₄P₆O₂₄ Composite Solid Electrolyte and Newer Insight into the Mg²⁺-Ion Conducting Properties Using Impedance Spectroscopy

Adamu

2016

J. Phys. Chem. C

“…51 In any case, since the crossover frequency is temperature dependent, it can be observed in Figure 6 that the crossover frequencies, p, shift towards high-frequency as temperature increases. Meanwhile, the logarithmic plot between dc-conductivity and crossover frequency, p, in Figure 8 insert gives a slope of 1 which agrees with conductivity formalism 50 , which implies that both dc-and ac-conductions are closely correlated and that they are of same mechanism 52 , alternatively, the characteristic angular frequency, p, is activated with the same thermal activation energy as dc-conductivity. 49,50,52,53 At high-frequency dispersion, angular frequency-dependent ac-conductivity, ac( ) increases and is well described by the Jonscher universal power law formulated as 45,54 ac…”

Section: Resultssupporting

confidence: 67%

Assessment of MgZr₄P₆O₂₄as a Solid Electrolyte for Sensing Mg in Molten Non-Ferrous Alloys

Adamu

Jacob

2020

J. Electrochem. Soc.

The potential solid electrolyte, MgZr4P6O24 was prepared using a modified sol-gel method. Both structural and electrical properties of the solid electrolyte were determined. DSC-TGA analysis indicated that pure dried xerogel when calcined at 900 o C converts to single phase MgZr4P6O24 nanopowder with good crystallinity. Pellets of 13mm diameter and 3.8mm thickness made by uniaxial compression were sintered at 1300 o C for 24h. XRD and HR-TEM indicated that the crystalline phase is monoclinic having crystallite size of approximately 40nm. The sintered pellets were stable in the temperature range from 1000 to 1300 o C, with minor extraneous peaks indicating traces of a coexistent second phase (Zr2P2O9) at the higher temperature. Using impedance spectroscopy, the electrical conductivity of MgZr4P6O24 was determined as 7.23 x 10-3 Scm-1 at 725 o C. MgZr4P6O24 pellet was successfully used for fabrication of a solid-state Mg-sensor for measuring Mg concentration in molten Al at 700±5 o C, with biphasic powder mixture of MgCr2O4+Cr2O3 as ceramic reference electrode in air. A linear dependence of emf on logarithm of Mg concentration was obtained. The results indicate that the transport number of Mg 2+-cation in MgZr4P6O24 is 0.85±0.03 at 700 o C. The solid electrolyte has likely applications in high-temperature electrochemical sensors.

“…The logarithmic plot between DC conductivity and cross-over frequency (u p ) shown as a solid line in the plot of the Fig. 7 inset gives a unity slope, which perfectly agrees with the AC conductivity formalism 15 implying that the DC and AC conductions are closely correlated with each other and that they are of the same mechanism 31 or that the characteristic angular frequency u p is activated with same thermal activation energy as the DC conductivity. 30,32 Non-linear tting (with a goodness of t $ 0.98) of data in Fig.…”

Section: Electrical Characterisationsupporting

confidence: 70%

New insight into the electrical properties and ion dynamics of screen printed NASICON thick films

Mudenda

2015

J. Mater. Chem. A

Although AC conductivity measurements of NASICON is well documented in literature, thick film conductivity and ion dynamic studies, important for planar, are scarcely reported. Most thick film measurements are performed using four point probe methods (DC method) and are quite limited in that, they cant give information on ion dynamics and cannot seperate contributions from grains, grain boundaries and electrode effects. However, in this paper we report the electrical properties of NASICON, x = 1.95 thick films of different thicknesses (20-32 µm), screen printed on alumina substrates, in light of ionic dynamics using the AC conductivity formalism. Surface resistivities of thick films from impedance data in the frequency range 0.1 ≤ f (HZ) ≤ 3.2 × 10 7 is obtained. Impedance Cole-Cole plots shows grain interior and electrode effects. The hopping frequency and AC/DC conductivity are thermally activated and show Arrhenius-type behaviour, with activation energies in the range of 0.44 ≤ E a (eV ) ≤ 0.46. Scaling in conductivity and Modulus shows that the relaxation mechanisms are independent of temperature and film thickness. Conductivity was independent of film thickness at high temperatures. SEM reveals that there is a minimum thickness for which NASICON on alumina substrate can be printed and used in high temperature planar electrochemical devices.