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Ferroelectric stuffs have a broad scope uses in industry, such as stuffs fabricating, automotive detectors and control systems, aerospace geographic expedition, and atomic power [ 1,2 ] . All ferroelectric stuffs are piezoelectric due to the “ self-generated polarisation ” . Some of them are good campaigners for electromechanical transducers due to their sensitiveness, cost and hardiness. Quartz, individual crystal SiO2, which can work up to 350 i‚°C, is one of the most widely used piezoelectric stuffs. Detectors are needed to work at high temperatures. However, the maximal operating temperature is limited by the “ Curie points ” , the ferroelectric-paraelectric passage temperature [ 3 ] . Therefore, ferroelectric stuffs with a high Curie points are desirable for high temperature piezoelectric applications. Some typical ferroelectric stuffs with high Curie point have been found, such as LiNbO3 ( Tc = 1150 C ) , lithium tantalate, LiTaO3 ( Tc = 720 C ) [ 4-7 ] .

The A2B2O7-type ferroelectrics, such as Sr2Nb2O7, Ca2Nb2O7, La2Ti2O7 and Nd2Ti2O7, have a provskite-like superimposed construction ( PLS ) [ 8, 9 ] , and are known for their super-high Curie points ( many are above 1300 oC ) [ 10-13 ] . Furthermore, most of them have a low insulator invariable, high coercive field. Hence, they could be used as high temperature applications. Due to their alone belongingss, there is a big sum of research focussed on the A2B2O7-type ferroelectrics to look into their construction, piezoelectric, dielectric invariable and coercive field.

Except the piezoelectric application, ferroelectrics can be used as informations storages. Ferroelectric stuffs have spheres, which can be reversed by an external electric field, and the sphere wall is much thinner than magnetic sphere wall, about 1/10 of it. Hence, it is hopeful to do smaller memories by ferroelectrics.

Chapter II. Ferroelectrics

Ferroelectricity of stuffs was discovered in 1921 [ 14 ] . Ferroelectric stuffs have a self-generated polarisation untill chilling below the Curie point. In the 1950 ‘s, a immense moving ridge in the research of ferroelectric stuffs leads to the widespread usage of BaTiO3 as capacitances and piezoelectric transducer devices. From so on, many other ferroelectric stuffs including PbTiO3, PZT ( lead zirconate titanate ) and PLZT ( lead La zirconate titanate ) have been developed and put into service for a assortment of applications [ 14 ] . The ferroelectric ceramics have been widely utilized in the countries of capacitances, not volatile memories, medical ultrasound imagination and actuators, informations storage and shows [ 14 ] .

Most stuffs can be polarized linearly with external electric field, which is called dielectric polarisation. Compared to this, some other stuffs polarize non-linearly and the dielectric invariable is a map of the external electric field. However, ferroelectric stuffs are have a self-generated polarisation. Fig.2.1 is a standard P-E hysteresis cringle of ferroelectric crystal.

Fig.2.1 P-E hysteresis cringle for typical ferroelectric stuffs [ 14 ]

The application of an external electric field to the piezoelectric crystal causes the polarisation to travel up with increasing E ( electric field strength ) untill electric supplanting D reaches point C. The polarisation does non changed after this point which indicates polarisation is saturated. When Tocopherol is reduced, polarisation does non travel back the same manner as it went up. The remanent polarisation ( Pr ) is the residuary polarisation left when the electric field ( E ) reaches nothing. Then, the E contraries and the polarisation becomes zero when E reaching at point F. In the Figure, the value of |OF| is Ec which is named the coercive field and it is the opposite electric field needed to do the polarisation to zero.

But normally a self-generated polarisation in the crystal or a grain is non uniformly aligned throughout the whole crystal. A part that has an oriented polarisation way is called a ferroelectric sphere. The part between two spheres is called sphere wall. If the way of the spheres is random, it is non possible to see the ferroelectric on macroscopically. This is because the effects of single spheres will call off each other and the net polarisation will be zero. Therefore, we need to punt the crystal under a strong DC field. The procedure, shown in Fig. 2.2, is called polling.

Fig. 2.2 A polycrystalline ferroelectric with random orientation of grains before and after punting [ 15 ] .

Compared to individual crystal, it is more hard to punt the polycrystalline ceramics which is consequence of the random orientations of the grains. The grains oriented in different waies restrict the motions of sphere walls under electrical poling, doing the Ec of ceramics much larger than the individual crystal [ 44,45 ] . On the other manus, the ceramics have more individual crystal-like belongingss when all of the grains are oriented in a well way. This can diminish Ec.

Valasek found the first ferroelectric ( Rochelle Salt ) in 1921 and there are now over 500 sorts of ferroelectric stuffs. It is a immense household, usually, they are classified [ 5 ] as followed.

1. Corner Sharing Octahedra Compounds

Corner sharing octahedra structured ferroelectrics are the most of import household of ferroelectrics. Perovskite compounds, Lithium niobate, Tungsten bronze type compounds are all included in the group. The standard construction is shown in the image, Bb+ is in the centre of the octahedra while all the O2- sited on the six point, and the place between the octahedra is occupied by Aa+ .

Fig.2.3. ( a ) A three-dimensional perovskite-type unit cell ( BaTiO3 ) ; ( B ) Network of O2- ions octahedra in the construction [ 18 ] .

2. Compounds Incorporating Hydrogen Bonded Radicals

3. Organic Polymers

4. Ceramic polymer complexs

Chapter III. AnBnO3n+2 compounds

3.1. Structure and ferroelectric belongingss

AnBnO3n+2 compounds is one series of perovskite-related bed structured compounds ( PLS household ) which are assortments of the perovskite group.The PLS compounds include three series with the construction which looks like a consequence from cutting the three-dimensional perovskite construction along the [ 100 ] , [ 110 ] , [ 111 ] way by interpolation of extra O. The general signifiers of the three are A’Ak-1BkO3k+1, AnBnO3n+2 and AmBm-1O3m severally [ 9,19 ] .

In the AnBnO3n+2 expression, n represents the figure of BO6 octahedra that span one bed, and hence specifies the thickness of the PL ( perovskite-layer ) . Sometimes, n is non-integral due to the mixture of beds with different thickness and it indicates the mean figure of octahera per bed. In this construction alkaline Earth or lanthanide metals frequently occupy the A places while the B cations are normally titanium or niobium [ 8, 9, 19 ] . Some typical AnMnO3n+2 constructions are shown in Fig. 4.1.

Fig.3.1. skeleton diagram of the non-distorted crystal construction of all the members projected along a-axis.

All of the AnBnM3n+2 compounds infinite groups are either orthorhombic or monoclinic. Different crystal construction corresponds to different deformations of the beds relative to the ideal three-dimensional perovskite construction. In these systems, we can see that the typical deformations are leaning of the BO6 octahedra and supplanting of either or both the A and B cations [ 20 ] . Due to this, some of them have a symmetricalness construction while the others are non-centrosymmetrical.

There are many ferroelectrics in the PLS group. Same whole number ratio stuffs and their ferroelectric belongingss have been summarized in the Tables followed.

Table.3.1 A2B2O8, n=2 [ 19 ]

Table.3.2 A3B3O11, n=3 [ 19 ]

Table.3.3 A4B4O14, n=4 [ 9,19, 25 ]

Table.3.4 A5B5O17, n=5 [ 9,19 ]

Table.3.5 A6B6O20, n=6 [ 19 ]

Group n=3 is different from the other groups, this one can be divided into two smaller groups by the construction. One is made of three beds of perovskites and the other is made by a combination of n=2 and n=4 as shown in Fig. 4.2.

Fig.3.2. Structures of two members in n=3 ; One is mixed by n=2 and n=4 and another has consistent 3-octahedra-thick beds

In the group n=5, most of the stuffs are non ferroelectrics, an exclusion is Sr5Nb5O16 which is particular in this group. Though it does non look like AnBnO3n+2 in the expression, it can be considered as an oxygen-deficient n=5 type with ordered O vacancies [ 19 ] . Its construction is shown in Fig. 4.3.

Fig.3.3. Skeleton drawing of Sr5Nb5O16

From the image, we can see there are merely four beds of incorporate octahedra in the construction and could be included in the n=4 group. However it is in n=5 group in this article because its expression is closer to the n=5 stuffs.

From the informations above, it seems to be a general regulation that non-centrosymmetric infinite groups and ferroelectrics exist in the even types n=2, n=3 ( II ) , n=4 and n=6. On the other manus, in the uneven types n=3, n=5 radially symmetrical infinite groups and antiferroelectrics prefer to happen.

3.2. Lanthanum Titanate ( La2Ti2O7 )

The ferroelectric belongingss of La2Ti2O7 were first characterized in the 1970s [ 21-23 ] . At room temperature, La2Ti2O7 has been found to hold two alterations, one is monoclinic ( a=7.800 A , b=13.011 A , c=5.546 A , i?§=98.60iˆ i?? ) with infinite group P21 and the other is orthorhombic ( a=7.810 A , b=25,745 A , c=5.547 A ) with infinite group Pbn21 [ 25 ] . At 780 oC, the construction transforms into a 2nd orthorhombic system ( a=3.954 A , b=25,952 A , c=5.607 A ) with infinite group Cmc21. At 1500 i??C, it transforms into paraelectric system with infinite group Cmcm [ 24 ] .

Fig. 4.4 The construction of the Cmc21 alteration of La2Ti2O7 at 780 i??C projected along the a ( upper ) and c ( lower ) axes [ 24 ]

In Fig.4.5 and Fig.4.6, it is clear to see the structural alteration between the orthorhombic Cmc21 and monoclinic P21 alterations at 780 i??C. The alteration is characterized by supplantings of La atoms which takes topographic point within the several planes perpendicular to the a axis, and by rotary motions of TiO6 octahedra around axes parallel to the B axis and through the several Ti atoms [ 24 ] .

Fig.4.5 The linkages of TiO6 octahedra in the

P21 ( solid ) and Cmc21 ( dotted ) alterations.

Fig.4.6 A conventional drawing of structural alteration from the Cmc21 ( upper ) to the P21 ( lower ) alteration.

The construction of La2Ti2O7 is similar to other members such as Nd2Ti2O7 which is high Curie point ceramic excessively, but the d33 of La2Ti2O7 is higher at 2.6pC/N [ 25 ] .

Fig.4.4. Ferroelectric belongingss of textured ceramics. Polarizaiton-electric field ( P-E ) and current-electrical field ( I-E ) hysteresis cringles at 220A°C and 10Hz along the perpendicular way to the pressure for La2Ti2O7 [ 25 ]

This image shows the P-E and I-E hysteresis cringles of the La2Ti2O7 textured ceramics. It is clear to see current extremums matching to ferroelectric exchanging between 40 and 100 kV/cm [ 25 ] . The grains of textured ceramics have a general orientation shown in Fig. 4.5.

Fig. 4.5. Scaning electron microscope micrograph of the textured La2Ti2O7 [ 25 ]

After texturing, by and large, most of the grains are plate-like and oriented. In a textured ceramic, the ferroelectric belongings is perpendicular the orientated way. And there is no ferroelectric exchanging extremums along the way [ 25 ] .

3.3. Strontium Tantalite ( Sr2Ta2O7 ) and Strontium Niobate ( Sr2Nb2O7 )

Compared to Lanthanum Titanate, Sr2Ta2O7 has a really low ferroelectric stage passage temperature ( -107oC ) . Hence it is a paraelectric stage at room temperature. It has orthorhombic symmetricalness with infinite group Cmcm. The infinite group Cmcm has the highest symmetricalness of all the PLS A2B2O7 compounds. Therefore, the crystal construction of Sr2Ta2O7 at room temperature is expected to be a paradigm for these A2B2O7 compounds [ 26 ] . Though Sr2Nb2O7 has a similar construction to Sr2Ta2O7, it has a really high Curie point of 1342 oC. The crystal system is orthorhombic with infinite group of Cmc21 and lattice parametric quantities a=3.933 A , b=26.726 A , c=5.683 A [ 27 ] .

The crystal construction of Sr2Ta2O7 viewed along a and hundred way is shown in Fig. 4.6. The construction is radially symmetrical, which explains the paraelectric character of Sr2Ta2O7 at room temperature [ 26 ] . And the construction of Sr2Nb2O7 has been shown in Fig.4.8.

Fig.4.6. The crystal construction of Sr2Ta2O7 viewed ( a ) along a ; ( B ) along hundred way [ 26 ] .

The D-E hysteresis cringle of Sr2Ta2O7 c-plate crystal was measured at -190 oC ( see Fig. 4.7 ) . The self-generated polarisation Ps, remanent polarisation Pr and coercive field at a maximal applied field E0=6.8kV/cm were: Ps=1.9AµC/cm2, Pr=0.69AµC/cm2, Ec=0.4kV/cm, severally [ 10 ] .

Fig.4.7. D-E hysteresis cringle of Sr2Ta2O7 c-plate crystal at -190 oC and 50Hz [ 10 ] .

Fig.4.8. The crystal construction of Sr2Nb2O7 viewed ( a ) along a and ( B ) along degree Celsius

way [ 27 ] .

The chief difference between Sr2Ta2O7 and Sr2Nb2O7 construction is in the grade of distortion of the perovskite-like beds. Unlike the regular agreement in Sr2Ta2O7, the agreement of O atoms in Sr2Nb2O7 is mostly distorted from that in the ideal perovskite construction. The supplanting of Nb atoms from the Centres of NbO6 octahedra has z constituents every bit good as Y constituents, as is illustrated in Fig.4.9. Consequently, the crystal becomes non-centrosymmetric in this manner. In these constructions, B ions can displace easy along the degree Celsius axis, so, normally, the self-generated polarization is besides directed along the degree Celsius axis [ 26 ]

Fig.4.9. ( a ) The supplantings of Ta atoms and ( B ) Nb atoms from the Centres of several octahedral [ 26 ] .

Fig.4.10. D-E hysteresis cringle of Sr2Nb2O7 c-plate crystal at room temperature and 50Hz. Ps=9AµC/cm2, Pr=7 AµC/cm2, Ec=6kV/cm at maximal applied field E0=25 kV/cm [ 28 ] .

For Sr2Nb2O7, its ferroelectric belongings has been found in both individual crystal and ceramics. And the Sr2Nb2O7 household movie has potency to utilize as ferroelectric memory due to the low insulator invariable, low coercive field and high heat-resistance. The D-E cringle is shown in Fig.4.10.

3.4. Calcium Niobate ( Ca2Nb2O7 )

The construction of Ca2Nb2O7 is similar to La2Ti2O7 and Nd2Ti2O7. At room temperature, it has two alterations and one is monoclinic with infinite group P21 while the other is orthorhombic with infinite group Pbn21. The projections of the construction along the a and degree Celsius axes are shown in Fig.4.11 and Fig.4.12 [ 29 ] .

Fig.4.11. The construction of monoclinic Ca2Nb2O7 projected along the a axis [ 29 ] .

Fig.4.12. The construction of monoclinic Ca2Nb2O7 projected along the degree Celsius axis [ 29 ] .

Ca2Nb2O7 has a really high Curie point above 1500 i??C which is assumed by the fact that no dielectric anomalousness was found up tp this temperature and 1MHz. P-E cringle is shown in Fig.4.13 [ 11 ] .

Fig.4.13. D-E hysteresis cringle of Ca2Nb2O7 c-plate crystal at room temperature and 50Hz. Ps=7AµC/cm2, Ec=65kV/cm at E0=160 kV/cm ) [ 11 ] .

3.5. Neodymium Titanate ( Nd2Ti2O7 )

Compare to La2Ti2O7, Nd2Ti2O7 has higher Curie Point of approximately 1755K. The individual crystals of Nd2Ti2O7, which were prepared by the drifting zone technique, has first-class ferroelectric and piezoelectric belongingss: Ps=9I?C/cm2, Ec=200kV/cm, d22=6.5 pC/N [ 42,12,13 ] .

At room temperature, Nd2Ti2O7 has infinite group P21 and a monoclinic construction with lattice parametric quantities a=13.02 A , b=5.48 A , c=7.68 A and I?=98i??28i‚?i?›iˆ±iˆ?iˆ¬iˆ±iˆ?i??iˆ®

Nd2Ti2O7 ceramics can be prepared by sintering the assorted oxide path ( Nd2O3 and TiO2 ) [ 43 ] in air from 1300 oC to 1500 oC. Fig.3.5.1 shows the addition of dielectric invariable with the addition of sintering temperature and the duplicate sphere constructions bespeaking the ferroelectric nature of Nd2Ti2O7 ceramics is shown in Fig.3.5.2.

Fig.3.5.1 Dielectric invariable of Nd2Ti2O7 as a map of sintering temperature at 1 kilohertzs [ 43 ]

Fig.3.5.2 The sphere construction in a individual grain of Nd2Ti2O7 sintered at 1450 oC [ 43 ]

3.5. Other A2B2O7 compounds

In the A2B2O7 group, there are still many other ferroelectrics, and they have non been decently characterized, such as Cd2Nb2O7, Ce2Ti2O7, Pr2Ti2O7. Actually, most of the A2B2O7 compounds can be divided into PLS ( perovskite-related bed construction ) and PS ( pyrochlore construction ) . The construction is dependent on the ratio of R ( Aa+ ) /r ( Bb- ) . Compared to PLS compounds, the pyrochlore structured material tends to be more stable with smaller A-site cations [ 30 ] . Lanthanide titanites Ln2Ti2O7 ( Ln=Sm-Lu ) with radius ratios 1.22 a‰¤ rLn3+/rTi4+ a‰¤ 1.5 crystallize in the pyrochlore construction. On the other manus, Ln2Ti2O7 ( Ln=La, Ce, Pr, Nd ) with radius ratios of the cations rLn3+/rTi4+ a‰?1.5 ) prefer the PLS construction. However, under high force per unit area conditions, Sm2Ti2O7 and Eu2Ti2O7 crystallize with the PLS construction [ 31 ] .

It is hard to fix Ce titanate ( Ce2Ti2O7 ) at high temperature, because Ce ( III ) compounds tend to organize the thermodynamically stable Ce ( IV ) when the temperature is above 400oC. For fixing Ce2Ti2O7 ( CTO ) compounds, CeO2 and Ti2O3 are discriminatory to be used as the starting stuffs. The mixture was placed in an Ar ambiance at 1200 oC [ 30 ] . Lichtenberg F. [ 9,19 ] has reported that the crystal is ferroelectric, but there is no more inside informations about its Curie point and P-E cringle.

From the studies, Praseodymium titanate ( Pr2Ti2O7 ) was synthesized from a stoichiomeric mixtures of Pr6O11 and TiO2 [ 32 ] . The pulverization mixture was calcinated at 850 i??C for 10 hours followed by 1150oC for 10 hours under inactive air conditions [ 39 ] . Differential thermic analysis ( DTA ) showed that Tc=1755i??C for Pr2Ti2O7 [ 33 ] .

Eu2Ti2O7 has a Curie point of 1100 i??C and the construction can change over from pyrochlore to PLS under 8GPa at 1747i??C [ 40 ] . In a recent paper [ 41 ] , Eu2Ti2O7 with PLS construction was synthesized successfully under ambient-pressure at 800i??C by utilizing EuTiO3 as the precurso.

Unit of measurements parametric quantities of some A2B2O7 have been listed in table.4.6

Table.4.6 [ 13,14 ]

Compounds

a ( A )

B ( A )

C ( A )

I’ ( Es )

Ca2Nb2O7

3.85

5.49

26.46

90

Sr2Nb2O7

3.96

5.70

26.78

90

Sr2Ta2O7

3.94

5.69

27.19

90

La2Ti2O7

3.91A-2=7.82

5.55

13.01

98.6

Ce2Ti2O7

3.88A-2=7.75

5.50

12.98

98.6

Pr2Ti2O7

3.86A-2=7.71

5.50

13.02

98.5

Nd2Ti2O7

3.84A-2=7.68

5.46

13.00

98.6

Sm2Ti2O7

7.61

5.42

12.98

98.4

3.6. ABO4 in AnBnO3n+2

In the AnBnO3n+2 PLS household, though n=4 group attracted so much attending due to their first-class ferroelectric belongingss, there are some other compounds which have possibility to be ferroelectrics. Such as CeTiO4, LaTaO4 in n=2 group ; Pr3Ti2TaO11, La3Ti2TaO11 in n=3 ( II ) group ; Nd4Ca2Ti6O20, Sr6Nd4Ti2O20, Ca6Nb4Ti2O20 in n=6 group.

In the n=2 PLS group, CeTiO4, LaTaO4 do non hold a centre of symmetricalness. The infinite group of CeTiO4 is Cmc21 with monoclinic construction. Shinya and Takahisa have reported the CeTiO4 can be prepared by oxidising of the Ce2Ti2O7, and in the procedure of tempering in air for 10 hours, the red-brown Ce2Ti2O7 converted into xanthous CeTiO4. It was found to exercise a comparatively high photocatalytic activity under seeable light irradiation ( I» & gt ; 420nm ) [ 34 ] , but there is no study about its ferroelectric belongingss.

LaTaO4 has two constructions orthorhombic and monoclinic. In the temperature scope 423K to 1470K, the orthorhombic signifier of LaTaO4 is stable and coexists with monoclinic LaTaO4 between 423K and 293 K. The big second-order nonlinear response indicates that orthorhombic LaTaO4 has a noncentrosymmetric construction. The self-generated polarisation in orthorhombic LaTaO4, which is assessed from the 2nd harmonic signal, is equal to 1.6muC/cm [ 35 ] . The orthorhombic LaTaO4 was prepared by hydroxide coprecipitation followed by calcination and the monoclinic construction can be made by calcinating pulverization mixures of La2O3 and Ta2O3 at 1200A°C for 10 hours [ 36 ] . The crystal construction is shown in Fig.4.14.

Fig.4.14. The construction of LaTaO4 along hundred axis [ 37 ]

3.7. A3B3O11 in AnBnO3n+2

In n=3 group, most of the stuffs that are formed by perennial 3 beds ( type I ) are non-ferroelectrics. But the mixed-layer perovskite-like compounds which are a mixture of two beds and four beds are possible to be ferroelctric ( type II ) .

Pr3Ti2TaO11, La3Ti2TaO11 are in n=3 ( II ) group, and both of them can be made by heat-treating coprecipitated hydrated oxides. The crystalline stuffs obtained by heat-treating precipitates with Ln: Titanium: Ta = 3:2:1 ( Ln = La, Pr, Nd ) at 1190-1370 K were found to dwell of Ln2Ti2O7-based superimposed perovskite-like stages with the general expression A4-xB4-xO14 ( x=0.18 ) . And the extra heat intervention of a higher temperature can do well-crystallized Pr3Ti2TaO11 and La3Ti2TaO11. For Pr3Ti2TaO11, the temperature is 1570K while 1670K for La3Ti2TaO11.

Both of Pr3Ti2TaO11 and La3Ti2TaO11 belong to a noncentrosymmetric infinite group P2cm and Pmc21 with orthorhombic constructions. Crystallographic information is been shown in Table.4.7 [ 38 ] .

Table.4.7 [ 38 ]

Yu.A.Titov and A.M.Sych evaluated the self-generated polarisation Ps for La3Ti2TaO11 and Pr3Ti2TaO11 ( 1.3 and 0.7 relation to La2Ti2O7 ) is 6mC/cm2 and 4mC/cm2 severally, and the Ps in La3Ti2TaO11 is higher than that in La2Ti2O7, because the stuffs contain the same perovskite beds as are present in the ferroelectric stuffs La2Ti2O7 and Pr2Ti2O7 [ 38 ] . But there is no literature to back up the rating. The structural theoretical account has been shown in Fig.4.15.

Fig.4.15. Structure of Ln3Ti2TaO11 ( Ln=La, Pr ) :

a. indistinguishable beds with n = 3 ; b. jumping beds with n=2 and 4

the solid and dotted lines delineate BO6 octahedraat x = 0.5 and 0, severally [ 38 ]

3.8. A6B6O20 in AnBnO3n+2

With increasing figure of the beds, it is hard to organize long ordination in the construction, so there are more defects and there is less incorporate ratio compounds in this group.

Nd4Ca2Ti6O20 is one crystal in the n=6 group. It is non-centrosymmetric monoclinic construction with Pna21 infinite group. The construction has been shown in Fig.4.16. And the crystallographic information is a=7.664A , b=36.64A , c=5.436A while V=1526A3 ; Z=4 [ 39 ] .

Fig.4.16. The construction of Nd4Ca2Ti6O20

The stuff can be made by Nd2O3, TiO2 and CaCO3. The three stuffs are used as get downing pulverization in the ratio Nd2O3: TiO2: CaCO3 = 2:6:2 and heat them at 1000EsC followed by an1800EsC sinter [ 39 ] .

Chapter IV. Proposed research

My proposed research will concentrate on the AnBnO3n+2 household to happen some high Ci point compounds with first-class ferroelectric belongingss. And the experiment includes several stairss which is shown in Fig.4.1

Fig.4.1 Flow chart of experiment

For the research, I began with Ce2Ti2O7 and Pr2Ti2O7 which are reported as ferroelectrics but no inside informations can be found about ferroelectric belongingss. And farther more, in the periodic tabular array of elements the Ce and Pr are between La and Nd which means the four have similar atomic radius and negatron construction. Nd2Ti2O7 and La2Ti2O7 have first-class high-temperature ferroelectric belongingss, so Ce2Ti2O7 and Pr2Ti2O7 are good campaigners. Particularly Pr2Ti2O7, it has a really high Curie point above 1770K reported by F. Lichtenberg [ 9.19 ] .

The CeO2, Pr2O3 and TiO2 pulverization are used as natural stuffs and blend them in conformity with the stoichiometric proportion followed heating to do the Ce2Ti2O7 and Pr2Ti2O7 pulverization. After this, the ceramics will be prepared for the belongingss test.

The 2nd phase is to dope Ce into Nd2Ti2O7 and La2Ti2O7 to happen the relationship between the pot elements and ferroelectric belongingss. I hope to acquire some general regulation between the microstructure and the belongingss which can explicate some phenomenon in this household. The last phase will be to try to bring forth some new ferroelectric stuffs in the AnBnO3n+2 household mixed by different octahedron beds.

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