**6. Effect of different rare earth oxides on the dielectric properties**

In previous sections, we have presented interesting particle size dependent colossal dielectric response along with MD effect in Er2O3 and Eu2O3 nano-glass composite systems. From the obtained results, there are colossal enhancement of dielectric constant and large MD effect in Er2O3 case [20], while those in Eu2O3 case, smaller responses were observed [39]. Obviously, the different electronic and magnetic properties for Er2O3 and Eu2O3 play a crucial role. However, these results suggest great promise in further systematic investigation to distinguish the mechanisms that contribute to colossal dielectric responses along with MD effect in other RE2O3:SiO2 nano-glass composite systems (RE2O3, RE *~* rare earth, a series of elements from La to Lu with stable RE3+) with different RE2O3 NPs size.The purpose of such study is to find amorphous high-*k* oxide candidates and MD effect with superior phase stability for gate dielectrics from a lineup of rare earth metal oxides embedded in SiO<sup>2</sup> matrix, and to find a sequential coupling between different constituents among these nano-glass composite materials.

Figure 12 illustrates the temperature dependent *ε*′ of the series of rare earth oxide NPs-glass composite systems calcined at 700o C in the absence of the magnetic field. Here, we concentrate the variations of temperature dependent dielectric behavior mainly on the 700<sup>o</sup> C calcined sample for the sake of clarity. Besides that, the possibility of formation of other rare earth oxide phase (e.g., RE2Si2O7) mixture with crystalline RE2O3 is ruled out at 700o C for low dopant concentration (0.5 mol%) [22]. Interestingly, RE2O3:SiO2 nano-glass composite systems in which RE ~ Sm, Gd and Er show colossal enhancement of dielectric constant (*ε*′ ~10<sup>3</sup> ) around room temperature. The nature of the variation of the (*ε*′-*T*) curves represents well-defined maxima and notable dielectric broadening around *ε*′m (maximum value of *ε*′) with high *ε*′ and different from pure bulk RE2O3.

22 Figure 12 illustrates the temperature dependent

) with high

and different from pure bulk RE2O3 6 .

m (maximum value of

5 the variation of the (

around 


max

(b)

'

21

35

bulk RE2O3 37 .

36 high

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

15

20 applied magnetic field. **Figure 12.** (Color online) The *ε*′-*T* curves of RE2O3 (gel-glass calcined at 700<sup>o</sup> C) at 1 kHz without applied magnetic field. 1 sake of clarity. Besides that, the possibility of formation of other rare earth oxide phase (e.g., RE2Si2O7) mixture with crystalline RE2O3 is ruled out at 700<sup>o</sup> 2 C for low dopant concentration (0.5 mol%) [22]. Interestingly, RE2O3 3 :SiO2 nano-glass composite systems in which RE ~ Sm, Gd and Er show colossal enhancement of dielectric constant (~10<sup>3</sup> 4 ) around room temperature. The nature of


of the series of rare earth oxide NPs-glass

constant (

) with


Figure 12. (Color online) The *ε*-*T* curves of RE2O3 (gel-glass calcined at 700o 19 C) at 1 kHz without

composite systems calcined at 700<sup>o</sup> 23 C in the absence of the magnetic field. Here, we concentrate the variations of temperature dependent dielectric behavior mainly on the 700o 24 C calcined sample for the


 promising high-*k* gate dielectrics due to its reproducible high dielectric constant (Figure 13(a)), single-stage process in air at moderate temperature and good compatibility with modern microelectronics processing technique. The present systems also show the MD effect around the transition temperature. The MDR at 1 kHz is plotted as a function of atomic number of the rare earth elements near *T*m as shown in the Figure 13(b). The RE2O3 35 :SiO2nano-glass composite systems in which RE ~ Sm, Gd, Er and Lu show colossal response of dielectric constant under applied magnetic field. Sol–gel process provides a convenient way for tailoring phase pure, self-organized NPs of nearly uniform sizes (particle size distribution histogram from TEM image) and for facilitating

Sm

56 58 60 62 64 66 68 70 72

Atomic number

Gd

Lu

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

Er2 O3

> Gd2 O3

H=0 T f : 1 kHz

of the series of rare earth oxide NPs-glass

C) at 1 kHz without applied magnetic

constant (

) with


Sm2 O3

150 200 250 300 350

14 **Ferroelectrics** 1 sake of clarity. Besides that, the possibility of formation of other rare earth oxide phase (e.g., RE2Si2O7) mixture with crystalline RE2O3 is ruled out at 700<sup>o</sup> 2 C for low dopant concentration (0.5 mol%) [22]. Interestingly, RE2O3 3 :SiO2 nano-glass composite systems in which RE ~ Sm, Gd and Er

*T* (K)

~10<sup>3</sup> 4 ) around room temperature. The nature of


Er

Figure 12. (Color online) The *ε*-*T* curves of RE2O3 (gel-glass calcined at 700o 19 C) at 1 kHz without

composite systems calcined at 700<sup>o</sup> 23 C in the absence of the magnetic field. Here, we concentrate the variations of temperature dependent dielectric behavior mainly on the 700o 24 C calcined sample for the 25 sake of clarity. Besides that, the possibility of formation of other rare earth oxide phase (e.g., RE2Si2O7) mixture with crystalline RE2O3 is ruled out at 700<sup>o</sup> 26 C for low dopant concentration (0.5 mol%) [22]. Interestingly, RE2O3 27 :SiO2 nano-glass composite systems in which RE ~ Sm, Gd and Er 28 show colossal enhancement of

 ~10<sup>3</sup> 29 dielectric ) 30 around room temperature. The 31 nature of the variation of the (

Sm

32 *T*) curves represents well-33 defined maxima and notable 34 dielectric broadening around

Nd

Sm

m (maximum value of

and different from pure

Gd

Eu

Gd

Eu

Sm

Eu

Dy

Dy

Ho

Ho

Dy

56 58 60 62 64 66 68 70 72

Atomic number

Gd

C with rare earth atomic number.

56 58 60 62 64 66 68 70 72

Atomic number

Gd

Eu

**Figure 13.** (Color online) (a) Maximum value of dielectric constant, and (b) MDR under 5 T applied field of RE2O3:SiO2

 Figure 13. (Color online) (a) Maximum value of dielectric constant, and (b) MDR under 5 T applied field of RE2O3:SiO2 nano-glass composite systems calcined at 700o 29 C with rare earth atomic number. The amorphous self-organized rare earth oxide nano-glass composite systems may be the promising high-*k* gate dielectrics due to its reproducible high dielectric constant (Figure 13(a)), single-stage process in air at moderate temperature and good compatibility with modern microelectronics processing technique. The present systems also show the MD effect around the transition temperature. The MDR at 1 kHz is plotted as a function of atomic number of the rare earth elements near *T*m as shown in the Figure 13(b). The RE2O3 35 :SiO2nano-glass composite systems in which RE ~ Sm, Gd, Er and Lu show colossal response of dielectric constant under applied magnetic field. Sol–gel process provides a convenient way for tailoring phase pure, self-organized NPs of nearly uniform sizes (particle size distribution histogram from TEM image) and for facilitating

Sm

Nd

Nd

Nd

*f:* 1 kHz

La

La

Lu

Yb

Yb

Lu

Tm

Yb

Yb

Tm

Er

Tm

Lu

Lu

Tm

Er

Ho

Ho

Er

Dy

101

**Figure 12.** (Color online) The *ε*′-*T* curves of RE2O3 (gel-glass calcined at 700<sup>o</sup>

show colossal enhancement of dielectric constant (

) with high

and different from pure bulk RE2O3 6 .

H = 0 T

*f:* 1 kHz

m (maximum value of

102

'

190 Ferroelectric Materials – Synthesis and Characterization

22 Figure 12 illustrates the temperature dependent

5 the variation of the (

around 



MDR (%)

nano-glass composite systems calcined at 700<sup>o</sup>

0

40

(b)

*f:* 1 kHz



MDR (%)

La

0

40

(b)

101

102

103

(a)

H = 0 T

*f:* 1 kHz

La

101

max

'

102

103

'

max

(a)

20 applied magnetic field.

field.

21

35

bulk RE2O3 37 .

36 high

103

 La2 O3 Nd2 O3 Sm2 O3 Eu2 O3 Gd2 O3 Dy2 O3 Ho2 O3 Er2 O3 Tm2 O3 Yb2 O3 Lu2 O3

15

The amorphous self-organized rare earth oxide nano-glass composite systems may be the promising high-*k* gate dielectrics due to its reproducible high dielectric constant (Figure 13(a)), single-stage process in air at moderate temperature and good compatibility with modern microelectronics processing technique. The present systems also show the MD effect around the transition temperature. The MDR at 1 kHz is plotted as a function of atomic number of the rare earth elements near *T*<sup>m</sup> as shown in the Figure 13(b). The RE2O3:SiO2nanoglass composite systems in which RE ~ Sm, Gd, Er and Lu show colossal response of dielectric constant under applied magnetic field. Sol–gel process provides a convenient way for tailoring phase pure, self-organized NPs of nearly uniform sizes (particle size distribu‐ tion histogram from TEM image) and for facilitating homogeneous dispersion of these metal-oxide NPs in the silica matrix. It is believed that the sol–gel derived NP-glass composite systems prepared and calcined in identical condition (Figure 1(b)), the particle size distributions of all rare earth oxide at specific calcined temperature is nearly equal (say 700o C, we have checked for Er, Eu, Gd and La systems). These rare earth oxide NPs are rigidly fixed within the insulating silica matrix at all temperatures. So this dielectric behavior does not arise from the physical motion of the NPs. This feature takes place inside the rare earth NPs grain and they are very much conditioned by magnetic property of NPs grain, the potential barriers in the grain boundaries, the degree of deformation of the lattice and the crystallites, as well as the grain size and their constituent host. Why RE ~ Sm, Gd and Er shows much larger effects than other rare earths? It needs further investigation using magnetic and non-magnetic rare earth oxide NPs together with different doping concentra‐ tions to explore the mechanism and application feasibility on these rich dielectric materials.
