Publishable summary
Abstract: The main objectives proposed in this project have been achieved and the results
published and disseminated in the most appropriate platforms. The main results for each
task are summarised as:
Objective 1: Synthesis of new ceramic oxides via soft chemistry procedures
Task 1: Synthesis of new materials
The synthesis of different families of Li-conductors has been performed via the nitrate-citrate
route. Specifically, the following families have been prepared after several trials: Perovskite
type Li3xLa2/3-xTiO3-d (x=0.11 LLTO), Perovskites of composition Li3xLa2/3-xTi1-yMg yO3-d (x= 0.11
and y=0.05 and 0.1), Garnets Li7-3xGax□2xLa3Zr2O12 (where □ represents a vacancy and x=
0.15, 0.2 and 0.3), Garnets Li7-2xZnx□xLa3Zr2O12 (where □ represents a vacancy and x= 0.15,
0.2 and 0.3). Garnets Li7-4xGex□3xLa3Zr2O12 (where □ represents a vacancy and x= 0.05 and
0.1) and Pyrochlore based materials of composition ASbTeO6 (A= K, Li and H3O).
Objective 2: Study of the factors governing the transport properties
Task 2: Structural, Chemical and Thermal analysis
The purity of all the phases under study was assessed by X-ray diffraction (XRD)
measurements. In all the cases, the synthesis conditions were optimised to obtain single
high purity phases with the desired crystal structure. Rietveld refinement of the data was
performed with the Fullprof program to evaluate crystal structure features. We have also
analysed the chemical composition of the samples by inductively-coupled plasma optical
emission spectrometry (ICP-OES). The theatrical stoichiometry of the samples was
confirmed within the limits of the technique. Furthermore, 1H, 7Li and 71Ga magic angle
spinning nuclear magnetic resonance (MAS-NMR) was used evaluate the different cation
populations, chemical environments and mobility. Neutron powder diffraction (Fig. 1) was
used to analyse the crystal structure features of the materials and to analyse the Li location
and mobility.
a)
b)
30
25
Tof NDP
dry O2 Li6.4Ga0.2□0.4La3Zr2O12
Intensity (a.u)
20
15
10
5
0
-5
-10
40000
60000
80000
100000
120000
2 ()
Figure 1. a) Crystal structure and Li-vacancies-Ga localization, b) Neutron powder diffraction pattern
for Li7-3xGax□2xLa3Zr2O12 refined in the cubic Ia3̅d space group
Task 3. Electrical characterization
Impedance spectroscopy measurements have been performed using a Solartron 1260A
impedance/gain-phase analyser. The impedance data were collected using the Z-plot
software from 10 MHz to 1 Hz at open circuit voltage using the two electrode configuration
and with a signal amplitude of 50 mV (Fig 2.)
d)
a)
b)
c)
Figure 2: a) Equivalent circuit used for the impedance data fitting. Nyquist plots of the LLTO samples
sintered in different atmosphere: LLTO-A (squares), LLTO-SA (circles) and LLTO-O (triangles) b)
obtained from 10 MHz to 7Hz and c) from 10MHz to 10 kHz. d) SEM images and particle size
distribution of LLTO pellets sintered
Task 4: Electron microscopy measurements and trace diffusion experiments
Scanning Electron Microscopy (SEM – SEM Quanta 200 FEG) operated in low vacuum
mode at a voltage of 20 kV was used to analyse the microstructure of the samples. The
grain shape and boundaries were revealed by thermal etching. The grain size distribution
was calculated with the software Estereologia from a 2500 m2 surface area (Fig. 2c).
Task 5: Tracer ionic diffusion measurements
In order to investigate the surface composition, the LLTO sample was analysed by low
energy ion scattering (LEIS). Fig. 3 shows the LLTO surface spectrum obtained by 3 keV
He+ scattering. The presence of the C peak after the oxygen plasma exposure suggests the
formation of a carbonate layer on the surface, as this would not be removed during the
cleaning procedure. A surface peak corresponding to La cations located on the A-site of the
LLTO perovskite appears at 2213 eV, although most of the surface would be covered by the
carbonate layer and other contaminants (e.g. Na), as indicated by the small surface peak.
The Ti atoms are then located underneath the AO plane termination of the LLTO perovskite
implying that both Li cation and cation vacancies might be exposed in the surface facilitating
the ion-exchange.
Figure 3. LEIS surface spectrum for 3 keV 4He+ ions scattered from the LLTO pellet. Dashed lines:
background components corresponding to the secondary ions sputtered from the sample surface
(grey line, exponential decay at low energies) and the atoms located at the sub-surface (green=Ti,
blue=La). Inset: Surface spectra corresponding to the bulk composition after Ar + sputtering.