The objective of this article is to show how experimental discoveries in atomic physics are logically connected, and we land up with the consistent theoretical explanation to the structure and stability of the atom. It is also shown that Bohr’s correspondence principle and Erhenfest’s adiabatic invariant hypothesis act as a guiding rules to this route. As a generalization to Bohr’s quantum condition, the Wilson-Sommerfeld quantization condition for multi-periodic system is presented with a derivation.

Let us begin our discussion by recalling the great discoveries (Bieser, 1998; and Milant’ev, 2004) of the 19th century, namely, spectral patterns (Johann Jakob Balmer, 1884), X-ray Radiation (Wilhelm Conrad Roentgen, 1895), radioactivity (Antoine Henri Becquerel, 1896), the electron (Sir Joseph John Thomson, 1897). These experimental discoveries led to the fact that there exists the smallest particle of matter (the so called atom) which cannot be seen with the naked eye, and which must have a stable structure. But, what is its structure? In the year 1898, Sir J J Thomson proposed that the atom is a uniformly positively charged sphere of matter with electrons embedded in it like raisins in a fruitcake to neutralize the positive charge as shown in Bieser (1998). In the years 1909-1912, Ernest Rutherford performed a-particle scattering experiment as shown in Bieser (1998). He concluded that the positive charge of an atom is concentrated in a very small region, known as the ‘nucleus’ (Bieser, 1998). The nucleus is heavy and positively charged. It attracts the light and negatively charged electrons by a force inversely proportional to the square of the relative distance. So, the electrons must revolve round the nucleus in order that they do not collapse on to the nucleus. Thus, Rutherford’s experiment led to the ‘planetary model’ of the atom with the electrons circulating the nucleus similar to the planets orbiting the Sun.

The question is: How stable is the structure proposed by Rutherford? The Newton’s laws of motion and the Coulomb’s law of electric force, the two pillars of classical physics, led to the fact that the atom is stable. On the contrary, the laws of electrodynamics, the other pillars of classical physics, led to the fact that the accelerated electric charges radiate energy in the form of electromagnetic waves, i.e., an electron moving in a curved path is accelerated and therefore, should continuously lose energy, spiraling into the nucleus in a fraction of a second emitting radiation continuously increasing the frequency (Bieser, 1998).

Physics Journal, Electrical Transport Properties, Transmission Electron Microscopy, Magnetotransport Data, Antiferromagnetic Semiconductors, Chemical Precipitation Method, Nanocrystalline Manganites, Perovskite Structure, Citrate-gel Method, Polycrystalline Perovskite Material, Debye Scherrer Formula.