FERROELECTRIC PHASE TRANSITION

FERROELECTRIC PHASE TRANSITION

Ferroelectric transition and the temperature dependence of the dielectric constant

The compound is preferably a material application is very important. Further, in the present

Work, we have studied the changes in the temperature of sodium dielectric

Dihydrogen phosphate. During the investigation found that the temperature

In the heating cycle of the change in permittivity shows a very sharp jump

Dielectric constant, wherein the compound reaches the value of 5600-420000

42C (Figure 1 and Figure 2) the temperature falls again at a temperature of 46 C to

51C. Cooling curves have almost the same properties, but with moderately low value

Dielectric constant and the peak is so sharp. Sharp increase in the dielectric constant

Has been described, based on the activation polarization of the ferroelectric and 0 0

At 46 ℃, 27 ℃ to 46 in the dielectric constant between the initial wave transition

0C structural imbalance is due to take place through the elimination of water molecules from

Compounds. Broad peak occurrence will be described based on the relaxation

Systems are generally due to heterovalent obstacles. Slight cooling cycle

Hysteresis and prolonged heating, based on the deviation of the results explained

(Annealing) of the sample, with the annealing has shifted transition temperature.KEYWORDS:

Ferroelectric phase transition, and crystal structure of the dielectric constant.

Brief introduction

Amorphous solid dielectric properties are very important materials scientists.

The dielectric properties of amorphous materials abnormal findings around the ceramic specimens 1943

Different groups of scientists around the world. Amorphous crystal ferroelectric activity reports

1945-46 Hippel and colleagues [1] independence by WUL and Goldman Sachs [2-3]. Since

Particularly sensitive to the structure of the character of the phenomenon feroelectricity, it is only logical,

Ferroelectric barium titanate found considerable efforts to expand your search 3

Ferroelectric materials in the same family. Search is certainly effective, because it leads to

Lead titanate ferroelectric active discovery, a compound of KNbO KTaO.These Curie point 333

Dispersed in a wide range of temperatures, and the temperature is characterized by the symmetrical

From the initial cubic perovskite lattice distortion very different.

The dielectric properties of single crystals have been studied extensively by the Merz, and [4]

Subsequent cross [5] and some other authors extended and improved by the Merz of the results obtained.

Obviously, the dielectric constant of BaTiO crystals from the temperature dependence, which is different 3

Correspond to different phases. Orthorhombic phase, which generally coincides with the polar axis of the crystal orientation of the domains of different mixtures, one might first think of the measured

The average value of the dielectric constant fluctuates around the target.

The structures of the compounds under investigation show its properties similar to the South wins

Disodium hydrogen orthophosphate [6] of the phase changes. Also observed that in some

Ferroelectric crystal having a dielectric response as a function of temperature, so that the width of the crystallization peak

Also referred to as the relaxation system. The origin of this behavior is still controversial, but it is the most likely cause

Barriers heterovalent [7,8].

In the compounds of sodium dihydrogen changes the dielectric constant and the phase change

Orthophosphate have been explained on the basis of the activation process and the ferroelectric polarization

0 0 0

At 46 ℃, and at 27 ℃ to 46 ℃ dielectric constant between the initial fluctuation is due to the transition

Eliminate the structural imbalance of water molecules occurs. Occurrence

Broad, generally due to the relaxation of heterovalent basis disorder has been explained

System, because it is the [6,8,9] disodium hydrogen phosphate case, orthophosphate, and tungsten bronze

Compounds [10 ~ 13]. Cooling cycle results in a slight deviation, based on the already explained

Hysteresis and prolonged heating (annealing) of the sample, the annealing will also transition

Temperature. Sample temperature sensitivity indicates valuable applications such as smart

The dielectric constant change with temperature gives the idea that it is applied

Ceramics.

Experiment

The compound has been sourcing, E. Merck (India), Mumbai. Chemical grinding into

Fine powder in an agate mortar, avoid direct sunlight, preferably most of the sample preparation

At night. Particle preparation and the compressor (Flextural Tester CAT

2 No.AIM 313, S.No.91070 the AIMILAssociated, India), pressure range 0-10 tons of weight / cm. Asuitable

2

The mold having a rectangular cross-sectional area of ​​the piston = 2.33 cm.

Abrasive particles has been done in order to obtain a smooth surface parallel to the electrode was used for

Formation. Is very soluble in water, therefore, instead of colloidal graphite, silver compounds

Coating the electrode material for polishing crystals introduced internal charge. These

Fees and strain will be deleted, this is what we do during the annealing of the sample. In this

Sufficient time to maintain in a suitable furnace at their melting points close to 2/3 of the treated pellets

(Generally 8-10 hours). To remove most of the non-renewable annealing, so this

The process is not necessarily do so. Formation of the electrode, using colloidal silver paint.

Sample holder containing particles into the furnace maintained such that it is located very close to the middle

Part of the furnace. A good quality precisely calibrated thermometer to record the temperature. This

Thermometer with the help of adjustable stand, in such a way that it contacts the metal part of the sample

Holders of record the exact temperature of the sample.

Using the usual alternative approach, that is an appropriate sample holder in the samples with and without

[14]. Sample holder directly fixed volume measurement unit (zenith medium 92A). Results and Discussion:

We have selected the sample of sodium dihydrogen phosphate in solid form

measurement.The compound of the formula is sodium hydride PO.2H2O. Its molecular weight is 156.01. 24

Solid is a colorless orthorhombic and refractive index of 1.4629. Density of crystalline form

1.91. The compound is very soluble in water, so, instead of colloidal graphite, silver paint

Electrode. During the heating cycle of the dielectric constant rate of temperature change shows a very

Significant increase in dielectric constant, wherein the compound reaches its value in the value 560,042,000

42C (Figure 1) the temperature, at a temperature of 46 to 51C down again. Cooling curve

Almost the same properties, but with a low dielectric constant values ​​and the appropriate peak is not clear

(Figure 2). Peak temperature the following data. The dielectric constant of the sample at low temperatures (27 ℃ and 41 ℃) in the range of fluctuation

May be due to elimination of two water molecules

 from the sample. In fact, to eliminate

Only disturbs the water molecules from the crystal's physical measurements, but also created

Crystal defects such as observed in the case of barium nitrate8. After the elimination of water molecules

Crystalline ferroelectric phase transition at 42 ℃, this may explain the Curie

France [12].

IST to transition and there is a certain lag. The dielectric anisotropy

I do not know the phase antipolarized. The reduction in temperature of about 45C show a common

Phenomenon. Clear that the nature of the increase of 42 degrees or less, the decline of about 45

NAH PO.2H O ferroelectric transition around this temperature. Spontaneous polarization 242

Measuring a phase change can be confirmed. Cooling curve is abnormal transition

Point, which may be due to prolonged heating (annealing) of the sample, the annealing will also

Transition temperature.

Multi-domain liquid crystal compound the dielectric constant is detected by the temperature

Measurement of the compound. The free energy of the theoretical value calculated

Other functions may be determined from the data strictly speaking, the dielectric constant of such a nature

Compounds. The ferroelectric properties of the compound with a very sharp change in dielectric constant

Similar to the measuring of sodium nitrite (010) and (101) as a function of temperature [15-16].

The dielectric constant of more than 49 ° C, sodium dihydrogen phosphate, the Curie - Weiss law

Approximately (Figure 2) and the dielectric constant is inversely proportional to the difference between the reduced

Because of its temperature and the Curie temperature

Barium titanate [17] observed in the case. In fact, the transition ferroelectric sample

Nearly 35 ° C or so of development, due to structural phase transition around this temperature dipole moment

Development, as from its position to change the crystal, similar, as it is in the case of barium titanate active report the displacement of silver ions Wu Mei high [18]. Similar interpretation was given

Near the Curie temperature of the dielectric constant change in circumstances, lead nitrate [6], barium nitrate

[8]. Conclusion:

In this work, we conclude that the temperature change alters the structure, resulting in

The phase change compound and the active dipole sodium ions get enough kinetic energy

Energy faced obstacles. Dipole rotation and alignment are displayed in the ferroelectric

Compounds. Described the presence of a broad peak similar to the relaxation system, generally due to

To obstacles heterovalent. Sample temperature sensitivity indicates valuable applications

Smart dielectric constant variation with temperature to their ideas

Ceramics and intelligent application