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M_{2} = n^{6}p^{2}/ρV^{3}  acoustooptical quality factor. Its value is determined by the properties of the material  the refractive index n, the corresponding element of the elasticoptical tensor p_{ij}, the density ρ, the speed of sound V. This parameter is one of the most important for the overall assessment of the effectiveness of the acoustooptical material. The quality factor M_{1} = n^{7}p^{2}/ρV, M_{3} = n^{7}p^{2}/ρV^{2} and M_{4} = n^{6}p^{2}V/ρ^{3}, which characterize the performance of the acoustooptic device in cases where the maximum ultrasonic front length, conversion width and power density are limited, respectively, are also less frequently used. The DB gives M_{1} in cm^{2} *sec/g, M_{2} in sec^{3}/g and M_{3} in cm*sec^{2}/g.
Dielectric permittivity is a value that characterizes the dielectric properties of the medium  its response to an electric field. In the relation D = εE, where E is the electric field strength, D is the electric induction in the medium, the dielectric permittivity is the coefficient of proportionality ε. In most dielectrics at not very strong fields the dielectric permittivity does not depend on the field E. In strong electric fields (comparable to the intraatomic fields), and in some dielectrics (e.g., ferroelectrics), the dependence of D on E is nonlinear in normal fields. The value of dielectric permittivity depends significantly on the type of substance and on external conditions (temperature, pressure, etc.). In variable electric fields the dielectric permittivity depends on the frequency of the field dielectric permittivity.
The coefficient of attenuation of elastic waves B characterizes the loss of acoustic energy due to dislocation friction or interaction with conduction electrons and phononphon interactions, as well as the scattering of acoustic energy on lattice defects, etc. [1]. The DB is given in dB/cm.
The coefficient of linear thermal expansion α_{L} = l^{1}(dl/dT) _{p} К^{1} is the relative change in linear size of a body when heated by dT degrees at constant pressure [2].
In general, the coefficient of linear thermal expansion can be different when measured along different directions: α_{x}, α_{y}, α_{z}. For isotropic bodies α_{x} = α_{y} = α_{z}.
The linear electrooptical effect coefficient r_{ijk} determines the change in refractive indexes caused by the action of the electric field [1]. In the DB it is given in m/V.
The electromechanical coupling coefficient is defined as the ratio of the mutual elastic (U_{m}) and electric energy density to the geometric mean of the internal elastic U_{l} and electric (U_{d}) energy densities [1]:
k = U_{m}/(U_{l}  U_{d})^{2}.
k is measured as a percentage.
k_{31}  coupling coefficient, which corresponds to the resonance of oscillations along the length of the plate, having electrodes on the largest surfaces, the polar vector perpendicular to the largest planes.
k_{t}  coupling coefficient, which corresponds to the resonance of oscillations along the polar vector along the thickness of the plate having the electrodes on the largest planes.
k_{33}  coupling coefficient, which corresponds to the main resonance mode of oscillations along the polar vector along the length of the cylinder with the electrodes applied on its end surfaces.
k_{15}  coupling coefficient, which corresponds to the resonance of oscillations along the thickness of the plate, having electrodes on the largest surfaces, the polar vector lies in the plane of the plate.
Density is a value equal to the ratio of body mass to volume [3]. In the DB it is given in g/cm^{3}.
The refractive index is the ratio of phase velocities of light in the first and second isotropic media, respectively [4]. The ratio of velocities of propagation of optical radiation in the first and second media [5]. Optically anisotropic substances have double refraction: splitting of a refracting light beam into two beams propagating at different speeds. The optical properties of crystals of cubic syngony are characterized by a single value of the refractive index. Crystals of tetragonal, hexagonal and trigonal synergies are optically uniaxial, with the optical axis coinciding with the major axis of symmetry of the crystal. All directions, except for the optical axis, are characterized by two refractive indices: n_{o} is the index of refraction of the ordinary beam and n_{e} is the index of refraction of the extraordinary beam, which depends on the orientation. Crystals of rhombic, monoclinic and triclinic syngonies are characterized by three values of the refractive index: n_{a}, n_{b} and n_{c} [1].
Transparency Band  a region of optical radiation wavelengths in which it does not change the set of frequencies of its constituent monochromatic radiations and their relative intensities.
Piezoelectric constants are the coefficients d, e, g, h in the relations P_{l} = d_{lij}σ_{ij}, P_{l} = e_{lij}ε_{jk}, E_{l} = g_{lij}σ_{jk}, E_{l} = h_{lij}ε_{ij}. E_{l} is the vector of electric field strength, P_{l} is the vector of electric polarization, σ_{ij} is the mechanical stress, ε_{jk} is the mechanical strain. All piezoelectric constants are related to each other, so that when describing the piezoelectric properties of a crystal we can limit ourselves to only one, for example d_{lij} [1]. The following dimensions of piezoelectric constants are used in the DB: h_{lij}, 10^{9} N/Cl, g_{lij}, 10^{3} m^{2} /Cl; e_{lij}, Cl/m^{2}lij, 10^{12} Cl/N.
Solubility is the ability of a substance to form homogeneous systems with other substances  solutions in which the substance is in the form of individual atoms, ions, molecules or particles. Solubility is expressed by the concentration of the dissolved substance in its saturated solution [2]. In the DB, solubility is given in g/100 g of solution.
The speed of sound is the speed of movement in a medium of an elastic wave, provided that the shape of its profile remains unchanged [5]. In monocrystalline solids, the speed of sound depends on the direction of wave propagation relative to the crystallographic axes [5].
The tangent of the dielectric loss angle is the ratio of the real and imaginary dielectric permittivity [5].
Hardness is the resistance of a substance to fracture and the formation of permanent deformation when mechanical forces are applied to its surface [4]. The hardness according to Mohs is given in the database. In this scale, numbers in ascending order denote singlecrystalline substances (minerals) arranged in such a way that each subsequent one was able to leave a scratch on the previous one. The extreme substances in the Mohs scale are talc (the least hard substance) and diamond [4]. The DB also gives the Knoop hardness (in GPa) [1].
Boiling point is the temperature of equilibrium transition of liquid to vapor at constant external pressure [5]. In the DB the boiling point at atmospheric pressure is given in degrees Kelvin.
The Curie temperature is the temperature of the reversible transition of a crystal from the ferroelectric (polar) phase to the paraelectric (nonpolar) phase for ferroelectrics [1]. In the DB it is given in degrees Kelvin.
Melting temperature is the temperature of equilibrium phase transition of a solid to liquid state at constant external pressure [5]. In the DB, the boiling point at atmospheric pressure is given in degrees Kelvin.
Heat capacity is a value equal to the ratio of the amount of heat required to heat a body to the temperature difference of the body [3].
Thermal conductivity determines the amount of thermal energy transferred through a unit area per unit time at a unit temperature gradient [1]. The thermal conductivity coefficient in the DB is given in W/m*grad.
Specific heat capacity is equal to the ratio of the heat capacity of a substance to its mass [4]. In the DB, it is given in J/kg*K.
Elastic constants are coefficients of proportionality c_{ijkl} and s_{ijkl} in the equation of the generalized Hooke's law [1], in which for sufficiently small stresses σ_{ij} the strain ε_{ij} is proportional to the magnitude of the applied stress, i.e.
σ_{ij} = c_{ijkl}ε_{kl},
i, j, k, l = 1, 2, 3.
Hooke's linear law can be written in inverse form:
ε_{kl} = s_{ijkl}σ_{ij}
c_{ijkl}  elastic stiffness constant (in DB given in N/m^{2}).
s_{ijkl}  elastic stiffness constant (in the database given in m^{2}/H).
The elasticoptical constant (Pockels constant) is a quantity characterizing the dependence of the refractive index of a material on the elastic deformation. Elasticoptical constant p = (ε_{o}  ε) ε_{o}^{2}S, where ε_{o} and ε are dielectric permittivities of unperturbed and disturbed media respectively, S is the medium deformation [5].
1. Acoustic Crystals. Handbook. Blistanov A.A., Bondarenko V.S., Chkalova V.V. et al. Under the editorship of M.P. Shaskol'skaya. Under Ed. by M.P. Shaskol'skaya. M.: Nauka, 1982, 632 p. (in Russian)
2. Wikipedia.
3. Handbook of physical quantities. Edited by I.S. Grigoryev and E.Z. Meilikhov. Moscow: Energoatomizdat, 1991, 1232 p. (in Russian)
4. Stepin B.D. Application of the International System of Units of Physical Units in Chemistry. Moscow: Higher School, 1990, 96 p. (in Russian)
5. Physical Encyclopedic Dictionary. Edited by A.M. Prokhorov. M.: Sov.encyclopedia, 1983, 944 p. (in Russian)