The lattice period of most metals is. Lattice period

For the simplest ideal monatomic cubic lattice, this is simply the distance between neighboring atoms. In the general case, this is the smallest distance, when shifted by which the lattice exactly reproduces its original appearance, that is, in each of its nodes there are the same atoms as before the shift.

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See what “Crystal lattice period” is in other dictionaries:

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2.8 ¸ 6 Å.

91. The difference between the melting and crystallization temperatures of metals is calledcritical temperatures.

92. Basic heat treatment operations: tempering, normalization,annealingAnd

hardening.

93. Vacation can be high,averageAnd short .

94. Vacation troostite – finely dispersed mixtureferriteAnd cementite.

Match.

95. Metal: Conditional group:

1. magnesium; A. noble;

2. vanadium; B. heavy;

3. nickel; V. rare;

4. platinum; G. light;

1B; 2IN; 3G; 4A.

for its manufacture:

1. camshaft bushing; A. 60SHFA;

2. suspension spring; B. SCh10;

3. gear housing; V. Br.O4P4S17;

4. foundation slab; G. KCh30-6;

1IN; 2A; 3G; 4B.

97. Impurity in steel: Effect of impurity on the properties of steel:

1. phosphorus A. increases fragility when

2. sulfur low temperatures

3. B. manganese deoxidizes harmful impurities

4. silicon B. causes red brittleness

G. increases strength

1 A; 2IN; 3G; 4B.

98. Structural component of the crystal lattice:

iron-carbon steels:

1. ferrite; A. complex rhombic with

dense packing of atoms;

2. austenite; B. fcc, carbon atoms arranged

in the center of the cube faces;

3. cementite; B. BCC, carbon atom in the center.

1.IN; 2B; 3A.

99. Match the temperatures to the transformation lines of the Fe 3 C diagram:

1. 1499 °C; A. line of eutectic transformation;

2. 1147 °C; B. line of eutectoid transformation;

3. 727 °C. V. line of peretectic transformation.

1IN; 2A; 3B.

Title Possible contents

structure: carbon, %:

1. austenite; A. 0.8 ... 2.14;

2. ledeburite; B. 6.67;

3. perlite; V. 4.3;

4. cementite; G. 0.8;

1- A; 2 -IN; 3 - G ;4- B.

101. Critical point on the Fe-C diagram Temperature, °C:

for pure iron:

3. A 3 V. 1401

1- G ; 2- IN; 3-B; 4-A

Install correct sequence:

102. Hardening of U8 steel is carried out in the following sequence:

1. heated to a temperature of 760 °C;

2. cool in water;

3. cool in air;

4. kept in an oven at a temperature of 760 °C. 1-4-2-3.

103. Sequence of stages when carburizing parts in a solid carburizer:

1. placing the box in the oven and holding it for a set time;

2. cleaning the part from contamination;

3. filling the carburizer into the box;

4. isolation of surfaces that are not subject to cementation;

5. closing the box with a lid, coating the edges with fireproof clay;

6. cooling the box and removing the part;

7. placing the part in a box;

8. pre-machining 8-2-4-7-3-5-1-6

104. A polymorphic modification that is stable at lower temperatures is denoted by:

1. γ; 2. α; 3.δ; 4. β. 2-4-1-3

105. Indicate the structures in descending order of their hardness:

1. ferrite; 3. sorbitol;

106. Sequence of operations when nitriding parts:

1. mechanical processing to obtain the final size;

2. nitriding;

3. protection of areas subject to nitriding;

Determination of the parameters of a unit crystal cell in the form of a parallelepiped with edge length parameters a, b, c and with angles between the edges α, β, γ

Lattice constant, or, which is the same thing, the lattice parameter is the size of the elementary crystal cell of the crystal. In the general case, a unit cell is a parallelepiped with different lengths of edges; usually these lengths are denoted as a, b, c . But in some special cases of the crystal structure, the lengths of these edges coincide. If, in addition, the edges emerging from one vertex are equal and mutually perpendicular, then such a structure is called cubic. A structure with two equal edges at an angle of 120 degrees and a third edge perpendicular to them is called hexagonal.

Generally speaking, the parameters of a unit cell are described by 6 numbers: 3 edge lengths and 3 angles between edges belonging to the same vertex of the parallelepiped.

For example, the unit cell of diamond is cubic and has a lattice parameter 0.357 nm at a temperature of 300 K.

In the literature, all six lattice parameters are usually not given, only the average length of the cell edges and the type of lattice.

Unit cell volume

The volume of a unit cell can be calculated by knowing its parameters (lengths and angles of the parallelepiped). If three adjacent edges of a cell are represented as vectors, then the volume of the cell V equal (up to sign) to the triple scalar product of these vectors (i.e., the scalar product of one of the vectors and the vector product of the other two). In general

For monoclinic lattices α = γ = 90°, and the formula simplifies to

For orthorhombic, tetragonal and cubic lattices, the angle β is also 90°, so

Layered semiconductor heterostructures

The constancy of the lattice parameters of dissimilar materials makes it possible to obtain layered sandwiches of different semiconductors with a layer thickness of several nanometers. This method produces a wide band gap in the inner layer of the semiconductor and is used in the production of high-efficiency LEDs and semiconductor lasers.

Lattice parameter matching

Lattice parameters are important in the epitaxial growth of thin single-crystal layers of another material on the surface of another single crystal - a substrate. With a significant difference in the lattice parameters of the materials, it is difficult to obtain single-crystallinity and dislocation-free growth of the layer. For example, in semiconductor technology for growing epitaxial layers of monocrystalline silicon, sapphire (aluminum oxide single crystal) is usually used as a heterosubstrate, since both have almost equal lattice constants, but with different types syngony, for silicon - cubic diamond type, for sapphire - trigonal.

Typically, the lattice parameters of the substrate and the layer being built up are chosen so as to ensure a minimum of stress in the film layer.

Another way to match lattice parameters is the method of forming a transition layer between the film and the substrate, in which the lattice parameter changes smoothly (for example, through a layer of solid solution with gradual replacement of atoms of the substrate substance with atoms of the grown film, so that the lattice parameter of the solid solution layer at the film itself coincides with this film parameter).

For example, a layer of indium gallium phosphide with a band gap 1.9 eV can be grown on a gallium arsenide wafer using the interlayer method.

see also

Notes

1. R. V. Lapshin (1998). “Automatic lateral calibration of tunneling microscope scanners” (PDF). Review of Scientific Instruments. USA: AIP. 69 (9): 3268–3276.

1. Carry out X-ray measurements and calculations in accordance with paragraphs (1-10) of section 3.1.

2. Find the values ​​for each line of the radiograph and enter these values ​​in Table 2.6 in column 3.

Table 2.6

Calculation of lattice periods

3. Find a series of relationships and enter the values ​​in column 4.

4. By comparing the resulting series of numbers with a similar series given in Table 2.4, determine the type of crystal lattice whose period should be determined.

5. For the established type of crystal lattice, use Table 2.3 to determine the interference indices.

6. Using several (3-5) lines of X-ray diffraction patterns (with large angles if possible), determine the period of the crystal lattice using expression (3).

7. Construct a graph and extrapolate the value to .

8. Check the correctness of determining the type of crystal lattice by calculating the number of atoms per it using the formula

Where is the atomic weight of the substance under study; - unit cell volume; - density of the test substance; g – mass of 1/16 of the mass of an oxygen atom.

Table 2.7

Interplanar distances

Continuation of Table 2.7

Equipment, devices, materials

1. X-ray photographs of polycrystalline pure metals.

2. X-ray films, rulers.

3. Calculation tables.

1. Determine the substance based on the data on interplanar distances obtained by calculating the x-ray diffraction pattern.

2. Determine the period of the crystal lattice of the identified metal (performed as directed by the teacher).

Registration of results

Report submitted upon delivery laboratory work, must contain:

a) the purpose of the work;

b) a scheme for the formation of an X-ray diffraction pattern of polycrystals in a Debye chamber;

c) experimental results, summarized in tables 2.5 and 2.6.

7. Security questions

1. Errors that arise when determining the lattice period and interplanar distances and methods for eliminating them.

2. Methods of loading film in a Debye camera, their advantages and disadvantages.

Literature

1. Soloviev S.P., Khmelevskaya V.S. Physical and technical foundations of materials science. - Obninsk. IATE. 1990. 100 p.

2. Gorelik S.S., Rastorguev L.N., Skakov Yu.A. X-ray and electron diffraction analysis. – M.: Metallurgy. 1970. 368 p.

JOB No. 3

CONSTRUCTION OF STATE DIAGRAMS BY THERMAL ANALYSIS METHOD

Goal of the work

Familiarize yourself with the method of thermal analysis and experimentally construct a phase diagram.