Solid-State Synthesis: Controlling Phase, Defect and Dopant · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Firing solids on purpose

Science · Chemistry · ages 22-23
Name ______________________   Date ____________

  1. What is an interstitial defect?

    • An unoccupied normal atom or ion site
    • A different atom occupying a normal site
    • An extra atom between regular lattice sites

  2. Which description identifies a ceramic solid-state synthesis route?

    • Mix solid powders, then heat them to react
    • Dissolve all precursors and keep them unheated
    • Measure an existing crystal without reacting it

  3. Small defect populations can change a solid's color, strength, and conductivity.

    Circle one:   True   False

  4. Three Ca2+ ions replace three Zr4+ ions in an oxide. If missing O2- ions alone compensate the charge deficit, how many oxygen vacancies are needed?

    • Six oxygen vacancies in total
    • Two oxygen vacancies in total
    • Three oxygen vacancies total

  5. In a stated reducible oxide, low oxygen pressure creates oxygen vacancies compensated by mobile electrons. Which electronic change follows?

    • The mobile electron concentration decreases
    • The mobile electron concentration increases
    • The electron mobility must increase with the vacancy count

  6. A powder pattern has target peaks and reproducible extra Bragg peak positions. Holder and instrument signals have been excluded. What should be investigated?

    • A change only in the amount of unchanged target phase
    • The presence of an additional crystalline phase
    • Preferred orientation of the unchanged target phase alone

  7. A routine powder pattern matches the target phase. A student concludes that the oxygen-vacancy concentration is ideal. Which response is justified?

    • The phase match alone does not establish vacancy concentration
    • The phase match proves that no atom or ion is missing anywhere
    • The phase match proves that conductivity has its maximum value

  8. In a fixed volume of oxide, 80 acceptors each have relative charge -1. Only holes (+1) and oxygen vacancies (+2) compensate them. Vacancies rise from 10 to 25 at fixed temperature and hole mobility. How does hole conductivity change?

    • It falls to half its initial value
    • It rises to twice its initial value
    • It stays fixed because the acceptor count is unchanged
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Firing solids on purpose W1-mt_5gri5iZ0lV-s1

  1. An extra atom between regular lattice sites · Vacancy is missing, substitution is swapped, interstitial is squeezed between.
  2. Mix solid powders, then heat them to react · The ceramic route uses mixed solid powders and heating to promote diffusion and reaction.
  3. True · Some defect populations can affect optical, mechanical or transport properties. The effect depends on the defect and conditions; it is not always large.
  4. Three oxygen vacancies total · Each substitution has a relative charge deficit of 2. Three substitutions give a deficit of 6, balanced by three oxygen vacancies of relative charge +2.
  5. The mobile electron concentration increases · The stated vacancies are compensated by additional mobile electrons, so their concentration increases. The prompt does not establish a mobility increase.
  6. The presence of an additional crystalline phase · An additional phase or revised structure can explain extra peak positions. Amount and preferred orientation alone change intensities of the unchanged phase.
  7. The phase match alone does not establish vacancy concentration · Phase identification and vacancy concentration are different measurements. Detailed structural or other suitable measurements may be needed.
  8. It falls to half its initial value · Charge balance gives 60 holes initially and 30 finally. Fixed volume makes the hole concentration halve; fixed hole mobility makes hole conductivity halve.
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