**3. Experimental details**

*H O*<sup>2</sup>

3

Si-OH Si-OH Si-O-Si +® + (2)

Si-OH Si-OR Si-O-Si ROH +® + (3)

������ ��2� � ������ � ��� �1�

������ � ������ � ��������� � �2� �2�

������ � ������ � ��������� � ��� ���

**Wet gel** 

**Evaporation**

º

178 Ferroelectric Materials – Synthesis and Characterization

º

5 (b) Condensation (water/alcohol condensation):

6 (i) Water condensation:

7 (ii) Alcohol condensation:

temperature schedule [16] (Figure 1(b)).

**Metal alkoxide**

(a)

**solution Dopant** 

(b)

19 calcination process.

Alcohol condensation:

4 (a) Hydrolysis:

3 groups.

 º

 º

17 according to preselected calcination temperature schedule [16] (Figure 1(b)).

**Sol**

**Dense glass Xerogel**

**Salt of rare earth under acidic condition** 

0

400

Temperature (oC)

800

1200

**Hydrolysis Polycondensation**   The clear solutions without any precipitaion are prepared with the mixing of half amount of ethanol in alkoxide and the solution consisting of the specified amount of water with another half of the ethanol containing HCl and dopant. The mixure solutions continued stirring for 2–3 hours at room temperature. The clear solution was kept in pyrex beaker at the atmospheric condition for 7/8 days to form stiff monolithic transparent gel. Further, the gels were allowed to dry for 4–5 weeks at room temperature. The dried (liquid removed by thermal evaporation) monolith is termed as xerogel. The oven–dried gel (temperature range 100–200°C) still contains large concentration of chemisorbed hydroxyls. Heat treatment in the temperature range 500–800°C desorbs the hydroxyls, forming a stabilized gel. At 1000°C, it transformed to a dense glass. Heat treatments of samples were performed

18 Figure 1. (Color online) (a) Sol–gel process. (b) Gel–glass embedded with rare earth nanoparticle

**Figure 1.** (Color online) (a) Sol–gel process. (b) Gel–glass embedded with rare earth nanoparticle calcination process.

It is relevant to mention here the important findings of Raman spectroscopic studies including measurements of pore size, density and specific surface area on the densification of undoped

0 10 20 30 40 50 60 70

Relative time (Hrs)

1 There are two distinct chemical reactions involved in the sol–gel process, describing 2 Eqn.(1) for hydrolysis of the alcohol groups, Eqns.(2) and (3) for polycondensation of hydroxyl

Colossal dielectric and MD response of RE2O3 nanoparticles in SiO2 glass matrix

The clear solutions without any precipitaion are prepared with the mixing of half amount of ethanol in alkoxide and the solution consisting of the specified amount of water with another half of the ethanol containing HCl and dopant. The mixure solutions continued stirring for 2– 3 hours at room temperature. The clear solution was kept in pyrex beaker at the atmospheric condition for 7/8 days to form stiff monolithic transparent gel. Further, the gels were allowed to dry for 4–5 weeks at room temperature. The dried (liquid removed by thermal evaporation) monolith is termed as xerogel. The oven–dried gel (temperature range 100–200°C) still contains large concentration of chemisorbed hydroxyls. Heat treatment in the temperature range 500– 800°C desorbs the hydroxyls, forming a stabilized gel. At 1000°C, it transformed to a dense glass. Heat treatments of samples were performed according to preselected calcination

ºº

ºº

**Gelling**

**Dense glass embedded with nanoparticle**

Powder X-ray diffraction (XRD) of the sample was performed by using Cu- *Kα* radiation. To analyze the detailed structure of samples, an ultrahigh-resolution transmission electron microscopy (TEM) (Model: JEM-3010, JEOL) was employed of NPs embedded SiO2 glass matrix calcined at different temperatures. Impedance spectroscopic measurements with/ without magnetic field are carried out in the temperature range 150–350 K using LCR meter (Model E4980A, Agilent) in conjunction with laboratory built cryostat arrangement integrated to the physical properties measurement system (Model: 6000, Quantum Design). The mag‐ netization (zero-field-cooled and field-cooled conditions) and magnetic hysteresis measure‐ ments are performed using a SQUID magnetometer (Model: MPMS-XL, Quantum Design) with temperatures varying from 2 to 350 K with ±1.0 K thermal stability and equipped with a superconducting magnet producing fields up to ±60 kOe. The sample in the powder form was packed in polytetrafluoroethylene (PTFE) capsule, where sample mass was chosen in the range of 8 to 12 mg for obtaining a good signal-to-noise ratio. Room temperature extended X-ray absorption fine structure (EXAFS) experiments were carried out in fluorescence mode (very low concentration of RE3+) at the RE ~ Er/Gd/La *L*III-edge at the 17C beamline in the National Synchrotron Radiation Research Center (NSRRC), Hsinchu, Taiwan. The EXAFS analysis was based on a multiparameter single-scattering fit (by the FEFFIT code [19] and using standard IFEFFIT data analysis package) in the *R*-space from the first two coordination shells; the fitting in the *k*-space (*k*<sup>2</sup> -weighted *χ*(*k*) with a *k*-cut range from 2.5-8 Å-1) led to the same result. A reference sample of bulk RE2O3 (unsupported SiO2 glass matrix) was used as a model standard for determining co-ordination numbers and inter-atomic distances. In obtaining the EXAFS function *χ*(*k*), the background absorption features which were superimposed on the EXAFS oscillations were removed from the spectrum using spline fit to both the pre-edge and the postedge regions.
