Capacitor

Question 1

What is the efficiency of dielectric capacitors?

Answer 1

Efficiency (much lower than 100%)

Efficiency close to 100% is also mentioned

Question 2

List three applications of dielectric capacitors.

Answer 2

• Hybrid electric vehicles (HEVs)
• Medical defibrillator devices (7~10 J)
• Electrical weapon systems (>150 J)

Question 3

What is capacitance?

Answer 3

The ratio of the magnitude of the charge on either conductor to the magnitude of the potential difference

Question 4

What is the vacuum permittivity (ε0)?

Answer 4

ε0 = 8.85 × 10^-12 C²/Nm²

Question 5

What does the dielectric constant (relative dielectric permittivity) represent?

Answer 5

ε (dimensionless materials constant)

Question 6

What does energy density depend on?

Answer 6

Material and electric field

Question 7

What is dielectric strength?

Answer 7

Maximum electric field in a dielectric before breakdown

Question 8

Define a dipole.

Answer 8

Two equal charges separated by a distance

Question 9

What is a dipole moment (p)?

Answer 9

p = q * d, direction from -q to +q

Question 10

What happens to permanent dipoles in a dielectric material under an external electric field?

Answer 10

They partially align with the field

Question 11

What is the relationship between electric displacement (D), permittivity (ε), and polarization (P)?

Answer 11

D = εE + P

Question 12

What is the mechanism of electronic polarization?

Answer 12

Movement of electron clouds

Question 13

What does the complex dielectric constant (ε*) consist of?

Answer 13

Real part (ε’) and imaginary part (ε”), where ε* = ε’ + iε”

Question 14

What is Debye Relaxation?

Answer 14

The relaxation time distribution function satisfies a specific mathematical form

Question 15

What is the Curie temperature (Tc)?

Answer 15

The temperature above which ferroelectricity is lost

Question 16

What are ferroelectrics?

Answer 16

Materials having spontaneous electric dipoles that can be re-orientated by an applied electric field

Question 17

Describe the Landau Phenomenological Theory.

Answer 17

Under an external electric field, neglecting higher orders of polarization, it relates polarization to the electric field

Question 18

What is spontaneous polarization?

Answer 18

The electric dipole that is temperature dependent

Question 19

What does the term ‘morphotropic phase boundary’ (MPB) refer to?

Answer 19

The composition where PbZrO3:PbTiO3 undergoes a displacive phase transformation

Question 20

What is the significance of the dielectric constant in materials?

Answer 20

It is temperature dependent and affects the unit cell size

Question 21

Fill in the blank: The maximum electric field in a dielectric before breakdown is known as _______.

Answer 21

[dielectric strength]

Question 22

True or False: Ferroelectrics are typically centrosymmetric above the Curie temperature.

Answer 22

True

Question 23

What does the term ‘energy stored’ refer to?

Answer 23

The work done on the capacitor, represented by the integral of voltage and charge

Question 24

What effect does temperature have on the properties of ferroelectric materials?

Answer 24

It influences spontaneous polarization and the dielectric constant

Question 25

What occurs during cooling from high temperature in PZT?

Answer 25

The crystal structure undergoes a displacive phase transformation with atomic displacements of about 0.1 Å.

Question 26

What is the composition ratio of PbZrO3:PbTiO3 at the morphotropic phase boundary?

Answer 26

About 53:47.

Question 27

What do compositions near the morphotropic phase boundary exhibit?

Answer 27

Some of the highest piezoelectric coupling coefficients and maximum permittivity.

Question 28

What is believed to enhance the properties near the morphotropic phase boundary?

Answer 28

The coexistence of tetragonal and rhombohedral phases.

Question 29

What is the significance of polymorphic nanodomain design?

Answer 29

It enhances energy storage in RFEs.

Question 30

What materials are used for energy storage in the study?

Answer 30

Ferroelectrics, antiferroelectrics, and relaxors.

Question 31

What is the formula for electric energy stored in ferroelectrics?

Answer 31

U = Ue + Uloss.

Question 32

What is the energy density formula in the context of energy storage?

Answer 32

W = 0.5 * Q * V.

Question 33

What is the detailed composition of the La, Zr-doped (Bi1/2Na1/2)TiO3-BaTiO3?

Answer 33

((Bi1/2Na1/2)0.9118La0.02Ba0.0582(Ti0.97Zr0.03)O3).

Question 34

What is the efficiency of (100)-oriented thin films at 3500 kV/cm?

Answer 34

Approximately 95%.

Question 35

What is the energy density of (111)-oriented thin films at 3500 kV/cm?

Answer 35

154 J/cm³.

Question 36

What does HRTEM stand for in the context of the study?

Answer 36

High-Resolution Transmission Electron Microscopy.

Question 37

What kind of films are examined for P-E loops?

Answer 37

(100) film.

Question 38

What is the approximate η (efficiency) after 10^8 fatigue cycles?

Answer 38

~80%.

Question 39

What is the training data set used for ML prediction of ε and breakdown strength?

Answer 39

1210 experimentally measured ε and Tg.

Question 40

How many synthesizable polymers were predicted in the ML study?

Answer 40

11,000.

Question 41

Which polymers were selected for high-temperature capacitors?

Answer 41

SrBO2F, SrBO2F, and BSiO2F.

Question 42

What is the requirement for a stacked parallel plate capacitor?

Answer 42

Large energy density, high-temperature stability, low fatigue.

Question 43

What is the significant impact of capacitors in the TOYOTA Prius inverter unit?

Answer 43

They occupy ~35% of the inverter volume, ~25% of the weight, and ~25% of the cost.

Question 44

What is a major issue with presently available capacitors?

Answer 44

Their performance and lifetime degrade rapidly with increasing temperature.