high-temperature superconductors

Examples of high-temperature superconductors in the following topics:

• Temperature and Superconductivity

  • When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected.
  • Usually, conventional superconductors have critical temperatures ranging from around 20 K to less than 1 K.
  • High-temperature superconductors can have much higher critical temperatures.
  • For example, YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K; mercury-based cuprates have been found with critical temperatures in excess of 130 K.
  • Describe behaviors of a superconductor below a critical temperature and in a weak external magnetic field

• X-Ray Spectra: Origins, Diffraction by Crystals, and Importance

  • For example, current research in high-temperature superconductors involves complex materials whose lattice arrangements are crucial to obtaining a superconducting material.

• Dependence of Resistance on Temperature

  • Resistivity and resistance depend on temperature with the dependence being linear for small temperature changes and nonlinear for large.
  • Some materials can become superconductors (zero resistivity) at very low temperatures (see ).
  • The temperature coefficient is typically +3×10−3 K−1 to +6×10−3 K−1 for metals near room temperature.
  • The resistance of a sample of mercury is zero at very low temperatures—it is a superconductor up to about 4.2 K.
  • Compare temperature dependence of resistivity and resistance for large and small temperature changes

• Absolute Temperature

  • Absolute temperature is the most commoly used thermodyanmic temperature unit and is the standard unit of temperature.
  • Thermodynamic temperature is the absolute measure of temperature.
  • By using the absolute temperature scale (Kelvin system), which is the most commonly used thermodynamic temperature, we have shown that the average translational kinetic energy (KE) of a particle in a gas has a simple relationship to the temperature:
  • The kelvin (or "absolute temperature") is the standard thermodyanmic temperature unit.
  • Real gases do not always behave according to the ideal model under certain conditions, such as high pressure.

• Heat as Energy Transfer

  • The transfer of energy is caused by the temperature difference, and ceases once the temperatures are equal .
  • Heat is often confused with temperature.
  • For example, we may say the heat was unbearable, when we actually mean that the temperature was high.
  • Heat is a form of energy, whereas temperature is not.
  • Such a temperature increase is observed while cooking.

• Thermal Pollution

  • Thermal pollution is the degradation of water quality by any process that changes ambient water temperature.
  • When water used as a coolant is returned to the natural environment at a higher temperature, the change in temperature decreases oxygen supply, and affects ecosystem composition.
  • Water, with its high heat capacity, works extremely well as a coolant.
  • Elevated water temperature typically decreases the level of dissolved oxygen of water.
  • Many aquatic species will also fail to reproduce at elevated temperatures.

• Overview of Temperature and Kinetic Theory

  • Kinetic theory explains macroscopic properties of gases (such as pressure, temperature, and volume) by considering their molecular composition and motion.
  • Also, the temperature of an ideal monatomic gas is a measure of the average kinetic energy of its atoms, as illustrated in .
  • The kinetic theory of gases uses the model of the ideal gas to relate temperature to the average translational kinetic energy of the molecules in a container of gas in thermodynamic equilibrium .
  • In kinetic theory, the temperature of a classical ideal gas is related to its average kinetic energy per degree of freedom Ek via the equation:
  • Real gases do not always behave according to the ideal model under certain conditions, such as high pressure.

• Diffusion

  • Diffusion is the movement of particles from regions of high concentration towards regions of lower concentration.
  • Diffusion is the movement of particles move from an area of high concentration to an area of low concentration until equilibrium is reached .
  • Molecular diffusion, often called simply diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero.
  • The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of the particles.
  • Particles moving from areas of high concentration to areas of low concentration.

• Conduction

  • The heat flux thus depends on the temperature difference T=Thot−Tcold.
  • The temperature of the material is T2 on the left and T1 on the right, where T2 is greater than T1.
  • he molecules in two bodies at different temperatures have different average kinetic energies.
  • Collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions.
  • In contrast, a molecule in the higher temperature region (left side) has high energy before collision, but its energy decreases after colliding with the contact surface.

• Humidity, Evaporation, and Boiling

  • Because evaporation is inhibited by high humidity, we feel hotter at a given temperature when the humidity is high.
  • The amount of water vapor the air can hold depends on its temperature.
  • The liquid and solid phases are continuously giving off vapor because some of the molecules have high enough speeds to enter the gas phase, a process called evaporation; see (a).
  • Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures.
  • Vapor pressure increases with temperature because molecular speeds are higher as temperature increases.