My experimental work on the problem of solid-state phase transitions began in mid 50's in Moscow, USSR, in the laboratory headed by late A. I. Kitaigorodskii, a noted expert in organic crystals. It was continued in the Crystallophysics Laboratory, which I headed, of the USSR Academy of Sciences Institute of Biophysics, and then, after my emigration in 1977 to U.S.A., in New York University. The initial idea of the study was in line with the conventional views. Knowing that two crystal forms of simple organic substance p-dichlorobenzene were similar, with the unit cell parameters close to each other, it was decided to investigate the kind of "deformation" converting the initial structure into the resultant. Here I would like to tell to everyone whose views on the phase transitions were also incorrect: it was not my fault that the real nature of the phase transitions turned out profoundly different. The result was stunning: instead of "deformation", a growth of perfectly face-shaped single crystals was observed within the transparent solid medium. Moreover, they had arbitrary orientations notwithstanding the three-dimensional order of the medium. The theory was based on quite different premises and did not foresee these phenomena.

     The status of the theory of solid-state phase transitions appears to me a rare one, if not unique. Rapid progress of the modern science as a whole is beyond question and, at first glance, this may seem to hold true for its branch investigating solid-state phase transitions. In reality, however, this particular science rolls back from an erroneous to even more erroneous interpretation of the phenomenon it is to account for. This is a regress against the background of general scientific progress. Every time we are told that the phenomenon of phase transitions is even more complicated than it was thought to be. Many highly qualified and noted scientists contribute to this process by developing more and more sophisticated theories based on the same wrong assumptions to replace the previous simpler versions proved to be unsatisfactory. Yet, the regress is not total: there also is accumulation of facts that have already come into fundamental conflict with the theory. The divergence between the theory and experiment is so great that the theory cannot be patched any more to absorb evidence. It ignores evidence, and first of all that a solid-state phase transition is always a nucleation-and-growth, rather than a cooperative phenomenon.

     Is this generally unusual in science? In a sense, it is not. Scientific development proceeds by trial and error. An erroneous theory frequently tries to survive by modifying and complicating itself and diluting its original premises in the face of new evidence. What is, however, unusual in the case under consideration is that this resistance lingers already for many decades, while evidence is treated as if it were nonexistent. The consequences are ruinous for a large piece of solid-state physics owing to ramifications to many processes where solid-state rearrangements take place. One of the ramifications concerns ferromagnetism and ferroelectricity.

     For years I was pursued by the questions: How and why did this situation come into existence? My reflections have led me to conclude that there was a unique combination of circumstances:
     (1) The fascinating topic of crystal phase transitions always attracted attention of workers specialized in particular physical experimental techniques such as X-ray analysis, optical spectroscopy, neutron scattering, ESR, NMR, calorimetry, etc., as well as scientists in particular applied fields. Lacking an expertise specifically in the field of phase transitions, these workers, distinguished ones among them, not infrequently took initiative in interpreting the phenomenon in terms of "conventional wisdom".
     (2) In the early stages, physical metallurgists were especially active in developing the theory. But metals are the most difficult solids to investigate phase transitions; the suggested theories were based on the ideas not rooted in hard facts.
     (3) Even prior to any investigation, it is difficult not to succumb to the "self-evident" idea on cooperative orderly modification - a kind of distortion/deformation - of the initial structure into the resultant. Sometimes found structural similarity between the polymorphs bolsters such an approach.
     (4) Another idea, generally accepted as a matter of course, is that solid-state phase transitions are a subject of statistical mechanics. (In the catalogues of the U.S. scientific libraries the topic of phase transitions is presented as "phase transitions (statistical mechanics)"). This a priori mentality has resulted from two circumstances: (1) success of statistical mechanics in accounting for other physical phenomena and (2) statistical mechanics is the only tool a theoretical physicist has for treating phase transitions. These circumstances turned out to be so powerful that phase transitions, at least most of them, were assigned, no matter what, to occur under the action of fluctuations (phase fluctuations, fluctuations of order parameter, of density, of entropy, molecular fluctuations...). These fluctuations increase toward the "critical temperature" at which the phase becomes unstable and suddenly turns into the alternative phase. But in reality a solid-state phase transition has nothing to do with statistical mechanics on a "cooperative" level, as it is proven in this book.
     (5) Due to mere coincidence, some experimental data have a misleading appearance and can be easily (and were) misinterpreted as supporting the statistical-dynamical approach. Thus, measurements of some physical properties vs. temperature through the transition sometimes exhibit "anomalies" which are regarded as a manifestation of "critical dynamics" of phase transitions. Similarly, comparison of the initial and final crystal structures in some cases leads to the impression that the transition resulted from a cooperative distortion or deformation of the initial crystal, or from a displacement of the Bravais lattices. Sometimes found orientation relationship between the initial and final crystal structures was an additional argument in favor of a cooperative reformation between the interdependent structures. The real origin of all these truly confusing effects is elucidated in this book in all detail.

      The reader may be surprised to find different problems of solid-state physics combined in the title of this book. The fact of the matter is that they are surprisingly closely related. Crystal phase transitions turned out to be that neighboring scientific field which had to be clarified in order to lay down proper foundations of ferromagnetism and ferroelectricity. I could not miss the opportunity; this is why there is Chapter 4 in this book. Every detail of the molecular mechanism of phase transitions described in the previous chapters was found important. The result is the coherent unified picture accounting for both ferromagnetism and ferroelectricity, instead of the failed classical theories by Weiss and Heisenberg. Ferromagnetism and ferroelectricity cannot serve as the last resort for "critical phenomena" in a solid state any more.

      I expect the book to be relatively easy for reading and understanding. No sophisticated mathematics was required. The method employed usually involved collection and logical analysis of all facts, finding a self-consistent explanation and further its verification. The reader will discover that the phenomena of solid-state phase transitions, ferromagnetism and ferroelectricity are incomparably simpler than they were presented us previously. All processes can be imagined in the model form. Even a shadow of mystery is removed; no "continuous" transformations, no advance preparations of a phase to "flip-flop" into the different phase upon achieving the "critical point", no unexplained peaks of physical properties rocketing up into infinity...