Study of dielectric constant and Curie temperature measurement of ferroelectric ceramics.

Perovskite Structure: Perovskite is a family name of a group of materials and the mineral name of calcium titanate (CaTiO3) having a structure of the type ABO3. Many piezoelectric (including ferroelectric) ceramics such as Barium Titanate (BaTiO3), Lead Titanate (PbTiO3), Lead Zirconate Titanate (PZT), Lead Lanthanum Zirconate Titanate (PLZT), Lead Magnesium Niobate (PMN), Potassium Niobate (KNbO3), etc. having a cubic perovskite-type structure (in the paraelectric state) with chemical formula ABO3.As conventionally drawn, A-site cations occupy the corners of a cube, while B-site cations sit at the body center. Three oxygen atoms per unit cell rest on the faces. The lattice constant of these perovskites is always close to the 4 angstrom due to the rigidity of the oxygen octahedral network and the well-defined oxygen ionic radius of 1.35 angstrom. A practical advantage of the perovskite structure is that many different cations can be substituted on both the A and B sites without drastically changing the overall structure. Complete solid solutions are easily formed between many cations, often across the entire range of composition. Even though two cations are compatible in solution, their behavior can be radically different when apart from each other. Thus it is possible to manipulate a material's properties such as Curie Temperature or dielectric constant with only a small substitution of a given cation. All ferroelectric materials have a transition temperature called the Curie point (Tc). At a temperature T greater than Tc the crystal does not exhibit ferroelectricity, while for T less than Tc it is ferroelectric. On decreasing the temperature through the Curie point, a ferroelectric crystal undergoes a phase transition from a non-ferroelectric (paraelectric) phase to a ferroelectric phase. BARIUM TITANATE (BaTiO3, BT): Barium Titanate (BaTiO3) has a ferroelectric tetragonal phase below its curie point of about 120 deg C and a paraelectric cubic phase above Curie point. The temperature of the curie point appreciably depends on the impurities present in the sample and the synthesis process. In the paraelectric cubic phase, the center of positive charges (Ba2+, Ti4+) coincides with the center of negative charges (O2- ion), and on cooling below Tc, a tetragonal phase develops where the center of Ba2+ and Ti4+ ions are displaced relative to the o2- ions, leading to the formation of electric dipoles. As the BT ceramics have a very large room temperature dielectric constant, they are mainly used in multilayer capacitor applications. The grain size control is very important for these applications.
(Reference: SES Instruments Pvt. Ltd USER'S MANUAL)
N.B. This is not for the promotion of any company, this video, and the supplementary information is totally for education purposes.
Sample Barium Titanate (BaTiO3)
Diameter 11.04 mm
Thickness (t) 1.22 mm
Permittivity of Space (εo) 8.85 x 10^(-12) F/mSl
Sl Temp Capacitance
No C pF
1 20 No Data Taken
2 25 1208
3 30 1222
4 35 1227
5 40 1226
6 45 1224
7 50 1228
8 55 1239
9 60 1251
10 65 1265
11 70 1283
12 75 1305
13 80 1326
14 85 1350
15 90 1378
16 95 1415
17 100 1462
18 105 1539
19 110 1616
20 115 1703
21 120 1851
22 125 *
23 126 *
24 127 *
25 128 *
26 129 *
27 130 *
28 131 *
29 132 *
30 133 *
31 134 *
32 135 *
33 136 *
34 137 *
35 138 *
36 139 *
37 140 *
38 145 *
39 150 1750
40 155 1637
41 160 1540
42 165 1451
43 170 1356
* : Take the readings by watching the youtube video, you can pause, seek backward for better observation.

[@jayantasarkar1193]

Waste of time!!

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