**6.1 EPR measured and results**

The EPR spectrum were obtained for powder ferroelectric at 300 K. The EPR measures for the zero sample produce a spectrum with signals *R* and *C*, see **Figure 10**. The signal *R* had *g* ¼ 2*:*1295 at 317 *mT* field. The signal *C* had several values *g*<sup>∥</sup> ¼ 1*:*9194, *g*<sup>⊥</sup> ¼ 1*:*9355 and *giso* ¼ 1*:*9301. The intensity of signal *C* is low and this indicate that insipidus presence of the paramagnetic center. The signal corresponds to uniaxial local symmetry on the tetrahedral perovskite structure [12]. Even when the microwave power is increased there are no signals of saturation effects for all samples, this indicate that the paramagnetic center is stable and maintain their interaction neighbor stable.

The 1, 2 and 5 samples at 300 K and 77 K shows the same spectrum except the intensity increases from sample 2 to sample 5, the spectra for samples 2 and 5 are show in **Figures 11** and **12** respectively. For sample 1, the signal *B* had *gB*<sup>⊥</sup> ¼ 1*:*9731 and *gB*<sup>∥</sup> <sup>¼</sup> <sup>1</sup>*:*9441; the signal *<sup>B</sup>*<sup>∗</sup> had *gB*<sup>∗</sup> <sup>⊥</sup> <sup>¼</sup> <sup>1</sup>*:*9352 and *gB*<sup>∗</sup> <sup>∥</sup> <sup>¼</sup> <sup>1</sup>*:*9257 spectroscopy parameters. For sample 2, there are two signals *B* and *B*<sup>∗</sup> too showed in **Figure 8**, for signal *B* was obtained *gB*<sup>⊥</sup> ¼ 1*:*9720 and *gB*<sup>∥</sup> ¼ 1*:*9462 at 345*:*20 *mT* and <sup>350</sup>*:*<sup>31</sup> *mT* respectively magnetic fields. For signal *<sup>B</sup>*<sup>∗</sup> *gB*<sup>∗</sup> <sup>⊥</sup> <sup>¼</sup> <sup>1</sup>*:*9360 and *gB*<sup>∗</sup> <sup>∥</sup> <sup>¼</sup> 1*:*9204 at 352*:*14 *mT* and 355*:*00 *mT* respectively magnetic fields. When the Cr+3 substituted the Ti+4 ion, the tetragonality decreases [8].

The **Figure 13** shows the spectrum for sample 4 with the signals *B* and *B*<sup>∗</sup> too, but additionally shows the *G*, *H* and *DPPH* signals. For signal *B* the *gB*<sup>⊥</sup> ¼ 1*:*9762 and *gB*<sup>∥</sup> <sup>¼</sup> <sup>1</sup>*:*9424 at 344*:*<sup>74</sup> *mT* and 350*:*<sup>71</sup> *mT* respectively. For signal *<sup>B</sup>*<sup>∗</sup> *gB*<sup>∗</sup> <sup>⊥</sup> <sup>¼</sup> 1*:*9384 and *gB*<sup>∗</sup> <sup>∥</sup> ¼ 1*:*9189 at 351*:*43 *mT* and 355*:*00 *mT* respectively. The *G* signal had *gG* ¼ 2*:*0755 at 328*:*21 *mT*. The signal *H* had *gH* ¼ 2*:*1449 at 317*:*6 *mT* field. The signal for *DPPH* had *g* ¼ 2*:*0036 at 340 *mT* expected value for the EPR standard paramagnetic marker.

The analysis of EPR results start from chemical composition for ferroelectric *Pb*0*:*95*Sr*0*:*05ð Þ *Zr*0*:*53*Ti*0*:*<sup>47</sup> *O*<sup>3</sup> þ *x*%*wtCr*2*O*<sup>3</sup> from the spin electronic arrangements for

**Figure 10.** *Zero sample spectrum shows R and C signals.*

**Figure 11.** *EPR spectrum for sample 2. There are two signal groups B and B*<sup>∗</sup> *.*

**Figure 12.** *EPR Spectrum for sample 5.*

each element atom composition. The *Cr* had 1*s* <sup>2</sup> 2*s* <sup>2</sup> 2*p*<sup>6</sup> 3*s* <sup>2</sup> 3*p*<sup>6</sup> 4*s* <sup>2</sup> 3*d*<sup>4</sup> electronic arrangement with þ6, þ 5, þ3 and þ2 oxidation states. The chromium compounds with *Cr*þ<sup>6</sup> oxidation state are no paramagnetic, because the 1*s* <sup>2</sup> 2*s* <sup>2</sup> 2*p*<sup>6</sup> 3*s* <sup>2</sup> 3*p*<sup>6</sup> 4*s* <sup>0</sup> 3*d*<sup>0</sup> electronic configuration had no unpaired electron. The *Cr*þ<sup>5</sup> had 1*s* <sup>2</sup> 2*s* <sup>2</sup> 2*p*<sup>6</sup> 3*s* <sup>2</sup> 3*p*<sup>6</sup> 4*s* <sup>0</sup> 3*d*<sup>1</sup> electronic configuration with unpaired electron and 5*=*2, 3*=*2 and ½ spin state corresponding to low, medium and high spin respectively. For *Cr*þ<sup>3</sup> the spin states could be ½ and 3*=*2, corresponding to weak

*Paramagnetic Transitions Ions as Structural Modifiers in Ferroelectrics DOI: http://dx.doi.org/10.5772/intechopen.95983*

**Figure 13.** *EPR spectrum for sample 4.*

and medium crystalline field split respectively. The *Cr*þ<sup>2</sup> is no paramagnetic by the 1*s* <sup>2</sup> 2*s* <sup>2</sup> 2*p*<sup>6</sup> 3*s* <sup>2</sup> 3*p*<sup>6</sup> 4*s* <sup>0</sup> 3*d*<sup>4</sup> electronic configuration, i.e., had four paired electrons in d-orbital, this is because we have a octahedral crystalline structure into the perovskite structure that causes electronic levels split (Zero field splitting); this split have a high energy levels separation and the electrons unfollows Hund's rule, see **Figure 6(A)**, this causes that electrons stays at lowers energy levels, all this is because the experimental g-values are less than 2.00 for all spectrum, **Figure 10**–**13**. The other elements are not paramagnetic [19, 20, 24–26]. The titanium has 4þ the state oxidation (*Ti*<sup>4</sup>þ), and the lead state oxidation is <sup>þ</sup>2 (*Pb*<sup>2</sup><sup>þ</sup>), both elements have not uncoupled electrons and they cannot be detected by EPR. Only *Cr*<sup>3</sup><sup>þ</sup> or *Cr*<sup>5</sup><sup>þ</sup> signals are expected in the EPR spectrum.

From chemical composition *Pb*0*:*95*Sr*0*:*05ð Þ *Zr*0*:*53*Ti*0*:*<sup>47</sup> *O*<sup>3</sup> þ *x*%*wtCr*2*O*<sup>3</sup> with *x* ¼ 0*:*0, 0*:*1, 0*:*2, 0*:*4 and 0*:*5, to sites *B* the *Zr*<sup>4</sup><sup>þ</sup> is substitute for *Ti*<sup>4</sup><sup>þ</sup> and to sites *A* the *Sr*<sup>2</sup><sup>þ</sup> is substitute for *Pb*<sup>2</sup><sup>þ</sup> in perovskite structure of the material [1–4, 25–27]. Additionally, in **Figure 14** shows how *Cr* is introduced to substitute *Ti* in sites *B* for the samples [8, 25–27]. The sample zero no contained *Cr* and it was taken like the control sample or EPR blank sample.

The **Figure 15** shows the EPR spectrum for sample 0 at 300 K. The *R* signal is at 317 *mT* and *g* ¼ 2*:*0134. The *C* signal is axial *g*<sup>⊥</sup> ¼ 1*:*965 and *g*<sup>∥</sup> ¼ 1*:*9181; bout signals are small at noise level. Thus, the blank sample, whose chemical formula indicates that it should not give an EPR spectrum, shows the *R* resonance, which is

#### **Figure 14.**

*Perovskite structure for ferroelectric Pb*0*:*95*Sr*0*:*<sup>05</sup> *Zr*0*:*53*Ti*0*:*<sup>47</sup> *O*<sup>3</sup> <sup>þ</sup> *<sup>x</sup>*%*wtCr*2*O*<sup>3</sup> *with x* <sup>¼</sup> <sup>0</sup>*:*0*,* <sup>0</sup>*:*1*,* <sup>0</sup>*:*2*,* <sup>0</sup>*:*<sup>4</sup> *and* 0*:*5*.*

**Figure 15.**

*EPR spectra for 1, 5 and 4 samples at 300 K. the two B and B*<sup>∗</sup> *oblate axial signals are typical by powder samples with g*<sup>⊥</sup> > *g*<sup>∥</sup> *and hyperfine interaction a*<sup>0</sup> ¼ *A.*

due to *Fe*<sup>3</sup>þ, and the *C* axial signal corresponds to *Cr* spectrum. When the temperature is low to 77 K, the *R* signal disappears and the *C* signal decreases. The *Cr*in this sample comes as manufacturing impurity. The 1, 2 and 5 samples show at 300 K and 77 K the same line shape spectrum, and the intensity increase from 1 to 2 and to 5. The increased intensity is due to percentage increase of *Cr* from 1% to 2% and 5% because the area under curve absorption EPR is proportional to the number of paramagnetic ions [9–12]. The typical EPR spectrum for the samples 0, 4 and 5 with *g* values less to 2.00 were obtained, see **Figure 15**. The *DPPH* signal is at left to the spectrum this means that *Cr* paramagnetic ions are *d*<sup>3</sup> with low spin ½ of *Cr*<sup>3</sup><sup>þ</sup> [9–18]. This case is analogous for *Mn*<sup>4</sup>þ, *<sup>S</sup>* <sup>¼</sup> <sup>1</sup>*=*2 in the ferroelectric *Pb Ti* ð Þ , *Mn <sup>O</sup>*<sup>3</sup> [27] that is isoelectronic with *Cr*<sup>3</sup>þ. The low spin value of *<sup>S</sup>* <sup>¼</sup> <sup>1</sup>*=*2 is caused by the tetragonal distortion in the octahedral symmetry (Cr-O) that increase the crystal field factor Δ, like is shows in **Figure 6(A)** [9–12]. These results are compatibles with the photoluminescence results found by Yanez et. al. for the same compound [8].

The four features of the spectrum are explained with two *B* and *B*<sup>∗</sup> oblate axial signals typical by powder with *g*<sup>⊥</sup> > *g*<sup>∥</sup> and hyperfine interaction *a*<sup>0</sup> ¼ *A*. The parameters are summarized in **Tables 1** and **2**, corresponds to a system with *S* ¼ 1*=*2.



*Paramagnetic Transitions Ions as Structural Modifiers in Ferroelectrics DOI: http://dx.doi.org/10.5772/intechopen.95983*

#### **Table 1.**

*EPR parameters for B signal.*


**Table 2.** *EPR parameters for B*<sup>∗</sup> *signal.*

For each *<sup>B</sup>* and *<sup>B</sup>*<sup>∗</sup> signal corresponds one *Cr*<sup>3</sup>þ, with spin *<sup>S</sup>* <sup>¼</sup> <sup>1</sup>*=*2, which is substituting to *Ti*<sup>4</sup><sup>þ</sup> or *Zr*<sup>4</sup><sup>þ</sup> in *B* sites into the octahedral symmetry with tetragonal distortion (high symmetry) slightly different one to other [27]. One of these cells correspond to octahedron with *Cr*<sup>3</sup><sup>þ</sup> belong to crystalline cells localized into the ferroelectric grains, and the other belongs to crystalline cells on surface of the material grains. This interpretation is consistent with the interpretation published of the *B* and *B*<sup>∗</sup> sites distinguished of *Mn*<sup>4</sup><sup>þ</sup> in *PbTiO*<sup>3</sup> [27].

#### **6.2 Microwave power variation**

The microwave power was varied from 1mW to 40mW for the samples and there is no change for EPR spectrum. The intensity of all features of the spectrum increase due power increase without differentiation. No distortion of the line shape of spectra is detected either, so until 40 mW power there is no sample saturation [9–18]. Qualitatively the 1, 2 and 5 samples present the same spectrum, but the quantitatively the EPR parameters change, **Tables 1** and **2**.

In addition to signals *B* and *B*<sup>∗</sup> the spectrum of sample 4 shows the isotropic *G* and *H* signals located at *gH* ¼ 2*:*1449 and *gG* ¼ 2*:*0755 respectively. By having these signals *g* values greater than 2*:*00 but around to zone to *g* ¼ 2*:*00 and because they are anisotropic could be identified like two of three expected fine lines for *Cr*<sup>3</sup>þ, *s* ¼ 3*=*2, it present the Zeeman split in a little crystalline field [5, 10, 14]. The positive deviation sign of value 2*:*0036 is explained for considerable difference between excited energy levels in ground state by *Lx*, *Ly* and *Lz* operators [12–18].

The signals *B* and *B*<sup>∗</sup> in the EPR spectrum for sample 4 at 77 K no changes respect to spectrum at 300 K, **Tables 1** and **2** but in the region for *G* and *H* signal at 77 K a third isotropic line with *g* ¼ 2*:*0716 is resolved. The power variation study no shows changes line shape or line number or saturation effects at 300 K from 1 to 40 mW for this sample.
