Table of Contents

## Why face Centred tetragonal is not possible?

Symmetry for tetragonal is single four fold axis, which means we can get the same lattice if we rotate the unit cell by 90 degree along C-axis. In case of face centred tetragonal, symmetry number is greater and this symmetry is not considered for tetragonal crystal system.

**Why is there no body-centered hexagonal lattice?**

Either they are incompatible with symmetry or they can be reduced to smaller cells. Imagine/draw a hexagonal C face-centered cell. The resulting lattice is incompatible with the 6-fold symmetry.

### Why isn’t there a base centered cubic Bravais lattice?

Why can a face-centered cubic lattice not be redrawn as a body-centered tetragonal lattice? A base-centered cubic lattice can be redrawn as a primitive tetragonal lattice, therefore we do not include it in the list of Bravais lattices.

**Which lattice is not possible in any crystal?**

Although objects themselves may appear to have 5-fold, 7-fold, 8-fold, or higher-fold rotation axes, these are not possible in crystals. The reason is that the external shape of a crystal is based on a geometric arrangement of atoms.

## Why is there no end centered cubic space lattice?

In order to have end centered closed packing structure unit cell must possess vectors a≠b≠c, which is absent in case of cubic unit cell due to this cubic unit cell cannot possess end-centred closed packing. The highest symmetry possible for an end centered unit cell is tetragonal.

**How many lattice points are there in face Centred tetragonal?**

Answer: One unit cell of face-centered tetragonal has 8 lattice points are corners and 6 lattice points at faces, total 14 lattice points.

### Which lattice is not a Bravais lattice?

I. Honeycomb lattice (not a Bravais lattice): The Bravais lattice of a honeycomb lattice is a hexagonal lattice.

**Which lattice does not exist?**

A C-centered tetragonal Bravais lattice does not exist.

## Which of the following lattice is not possible?

Pentagonal lattice is not possible because the interior angle of a regular pentagon is 108∘ which is not an integral factor of 360∘.

**Why 2d pentagonal lattice is not possible?**

Lattice constants are the length, edges of principal axes, and angle between unit cells. Crystals do appear to have 5-fold symmetry but these symmetries are not possible. Crystals can only exist in the 2, 3, 4 or 6-fold rotational axis. Therefore, crystals cannot have 5, 7, 8, and other higher-fold rotational axes.

### What is the difference between face Centred and end-Centred unit cell?

A Face-centred unit cell the constituent particles are present at the corners and one at the centre of each face. An End-centred unit cell contains particles at the corners and one at the centre of any two opposite faces.

**Can cubic lattice have base Centred unit cell?**

Therefore, the bcc lattice can be considered as a unit cubic cell with two lattice points per cell….1.2. 4 Body-Centered Cubic (bcc) Lattice.

Element | Lattice Constant (A°) |
---|---|

Europium | 4.61 |

Iron | 2.87 (Fe also has fcc phase) |

Potassium | 5.23 |

Lithium | 3.50 |

## What are the symmetry points of a face centered cubic lattice?

From Table 3 we notice that for the face centered cubic (f.c.c.) lattice there are two symmetry points and two possible propagation vectors for simple antiferromagnetic ordering with k = H /2: (0, 0, 1) and ( 1 2, 1 2, 1 2) corresponding to the so-called type-I and type-II antiferromagnetic ordering, respectively.

**Is the hexagonal close packed lattice the same as the face centered lattice?**

The hexagonal close-packed lattice consists of the same numbers of tetrahedrons and pairs of spins as the face-centered cubic lattice. Moreover, pairs and lattice points also are overlapping figures of tetrahedrons in this lattice.

### Which is not a primitive or centred lattice?

A lattice being an infinite, symmetric and periodic collection of zero-dimensional nodes, rigorously speaking it is neither primitive nor centred. The expression ‘centred lattice’ has to be considered as a shortcut for ‘lattice whose conventional cell is centred’. Types of centred lattices

**How to calculate the multiplicity of a centred lattice?**

The ‘multiplicity’, m, of the centred cell is the number of lattice nodes per unit cell (see table). The volume of the unit cell, Vc = ( ac, bc, cc) is given in terms of the volume of the primitive cell, V = ( a, b, c ), by