The ministry of higher and secondary special education termez state university faculty of chemisrty and tech nology course-2 205-group tagaeva dilshoda physical chemistry

THE MINISTRY OF HIGHER AND SECONDARY SPECIAL EDUCATION TERMEZ STATE UNIVERSITY FACULTY OF CHEMISRTY AND TECH NOLOGY COURSE-2 205-GROUP TAGAEVA DILSHODA PHYSICAL CHEMISTRY

THE MINISTRY OF HIGHER AND SECONDARY SPECIAL EDUCATION TERMEZ STATE UNIVERSITY FACULTY OF CHEMISRTY AND TECH NOLOGY COURSE-2 205-GROUP TAGAEVA DILSHODA PHYSICAL CHEMISTRY

COURSE WORK

THEME: SECOND ORDER PHASE TRANSITIONS.

“If you ask me, “What’s your problem?”, I answer that as our child’s education and upbringing” SHAVKAT MIRZIYOYEV

THEME: SECOND ORDER PHASE TRANSITIONS

PLAN

INTRODUCTION

• MAIN PART

I.1. ABOUT PHASE TRANSITIONS

I.2. TYPES OF PHASE TRANSITIONS

I.3. SECOND ORDER PHASE TRANSITION

I.4. LANDAU THEORY OF SECOND ORDER PHASE TANSITION

• CONCLUSION
• MATERIALS

About Phase transition

• Phase transition is when a substance changes from a solid, liquid, or gas state to a different state. Every element and substance can transition from one phase to another at a specific combination of temperature and pressure.

Each substance has three phases it can change into; solid, liquid, or gas(1). Every substance is in one of these three phases at certain temperatures. The temperature and pressure at which the substance will change is very dependent on the intermolecular forces that are acting on the molecules and atoms of the substance(2). There can be two phases coexisting in a single container at the same time. This typically happens when the substance is transitioning from one phase to another. This is called a two-phase state(4). In the example of ice melting, while the ice is melting, there is both solid water and liquid water in the cup.

There are six ways a substance can change between these three phases; melting, freezing, evaporating, condensing, sublimination, and deposition(2). These processes are reversible and each transfers between phases differently:

• There are six ways a substance can change between these three phases; melting, freezing, evaporating, condensing, sublimination, and deposition(2). These processes are reversible and each transfers between phases differently:

Evaporating: The transition from the liquid phase to the gas phase

• Evaporating: The transition from the liquid phase to the gas phase

Freezing: The transition from the liquid phase to the solid phase

• Condensing:The transition from the gas phase to the liquid phase
• Sublimination: The transition from the solid phase to the gas phase
• Melting: The transition from the solid to the liquid phase
• Deposition: The transition from the gas phase to the solid phase
• Recombination: The transition from the plasma phase to the gas phase
• Ionisition: The transition from the gas phase to the plasma phase

TEMPERATURE Temperature can change the phase of a substance. One common example is putting water in a freezer to change it into ice. In the picture above, we have a solid substance in a container. When we put it on a heat source, like a burner, heat is transferred to the substance increasing the kinetic energy of the molecules in the substance. The temperature increases until the substance reaches its melting point(2). As more and more heat is transferred beyond the melting point, the substance begins to melt and become a liquid(3). This type of phase change is called an isobaric process because the pressure of the system stays at a constant level.

PRESSURE Pressure can also be used to change the phase of the substance. In the picture above, we have a container fitted with a piston that seals in a gas. As the piston compresses the gas, the pressure increases. Once the boiling point has been reached, the gas will condense into a liquid. As the piston continues to compress the liquid, the pressure will increase until the melting point has been reached. The liquid will then freeze into a solid. This example is for an isothermal process where the temperature is constant and only the pressure is changing.

FIRST ORDER PHASE TRANSITIONS

• First order phase transitions are also often associated with sudden volume changes; ice expands relative to the water it came from. This is unusual; most solids take up less space than their liquid counterparts. We often associate an order parameter with a phase transition. In a liquid the atoms or molecules are disordered in their arrangement, but at the transition, they suddenly become ordered. Thus a first order phase transition is associated with a discontinous jump in the order parameter.

SECOND ORDER PHASE TRANSITIONS

• Second-order phase transitions are also called "continuous phase transitions". They are characterized by a divergent susceptibility, an infinite correlation length, and a power law decay of correlations near criticality. Examples of second-order phase transitions are the ferromagnetic transition, superconducting transition and the superfluid transition.

In contrast to viscosity, thermal expansion and heat capacity of amorphous materials show a relatively sudden change at the glass transition temperature[7] which enables accurate detection using differential scanning calorimetry measurements. Lev Landau gave a phenomenological theory of second-order phase transitions.

In contrast to viscosity, thermal expansion and heat capacity of amorphous materials show a relatively sudden change at the glass transition temperature[7] which enables accurate detection using differential scanning calorimetry measurements. Lev Landau gave a phenomenological theory of second-order phase transitions.

Apart from isolated, simple phase transitions, there exist transition lines as well as multicritical points, when varying external parameters like the magnetic field or composition.

Landau theory second order phase transitioin

LEV DAVIDOVICH LANDAU

(1908-1968)

Landau theory second order phase transitioin

• At a second order phase transition, the order parameter increases continuously from zero starting at the critical temperature of the phase transition. An example of this is the continuous increase of the magnetization at a ferromagnetic - paramagnetic phase transition. Since the order parameter is small near the phase transition, to a good approximation the free energy of the system can be approximated by the first few terms of a Taylor expansion of the free energy in the order parameter.

MATERIALS

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• 8. Gotze, Wolfgang. "Complex Dynamics of Glass-Forming Liquids: A Mode-Coupling Theory."
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